I’m doing the Pandaria Trainer circuit regularly to level pets and alts during Pet Battle week.
Failsafe with a mechanical means they rez with 20% health after being killed. Three days now battling Courageous Yon my Iron Starlette has just died and stayed dead while next pet on the team becomes active.
Further proof that this is a bug, if I forfeit and heal up, then fight same trainer again, this time Starlette rezzes normally and keeps fighting.
I haven’t seen any such failure.
Of course, when a fail-safe fails, it fails, not by failing, but by failing to fail safe. 
I don’t see a Starlette strat on Xu-Fu’s, so I don’t know what you were doing, exactly, so can’t test the conditions.
What breed Starlette? At what point in the battle? Did you save a log?
To try to rule out something, are you using the Iron Starlette’s Explode ability?
Main reason I opened this thread is that I’ve been frequently using this same strategy successfully for at least a year and before Tuesday hadn’t ever seen the Starlette fail to rez.
P/P Iron Starlette using Wind-up, Toxic Smoke, Supercharge, name is Killer
H/H Anubisath Idol with Crush, Sandstorm, Deflection
Carry pet, at least level 8
Wind-up, Supercharge, Wind-up takes out first pet Piqua
Lapin comes in and hits Starlette who responds with Toxic Smoke.
Lapin burrows, Starlette uses Wind-up.
Lapin hits with Flurry. It’s not unusual for Starlette to die at this point but in the past always rezzed and got another hit in with Toxic Smoke.
Tuesday I assumed I’d made a mistake so just tried again a second time. Wednesday was paying attention and surprised when Starlette died prematurely; had to heal and try again. Thursday did get some screenshots of the Pet Battle log both first and second tries.
Don’t know how to download the logs so Saturday stitched together screen grabs I’d gotten during fight. Once again forfeited and healed and second try worked normally.
Thank you for the full log!
Took me a while, but I finally got the same effect
Round 1", – [1]
Squawk dealt 150 damage to your Iron Starlette.“, – [2]
Attack Reduction to your Iron Starlette.”, – [3]
Wind-Up applied Wind-Up to your Iron Starlette.“, – [4]
Round 2”, – [5]
Lift-Off applied Flying to enemy Piqua.“, – [6]
Supercharge applied Supercharged to your Iron Starlette.”, – [7]
Round 3", – [8]
Lift-Off dealt 380 damage to your Iron Starlette.“, – [9]
Flying fades from enemy Piqua.”, – [10]
Wind-Up fades from your Iron Starlette.“, – [11]
Wind-Up dealt 1705 damage to enemy Piqua.”, – [12]
Enemy Piqua died.“, – [13]
Supercharged fades from your Iron Starlette.”, – [14]
Flying fades from enemy Piqua.“, – [15]
Round 3”, – [16]
Lapin is now enemy active pet.“, – [17]
Round 4”, – [18]
Adrenaline Rush dealt 150 damage to your Iron Starlette.“, – [19]
Adrenaline Rush applied Adrenaline to enemy Lapin.”, – [20]
Toxic Smoke dealt 216 damage to enemy Lapin.“, – [21]
Toxic Smoke applied Toxic Smoke to enemy team.”, – [22]
Toxic Smoke dealt 67 damage to enemy Lapin.“, – [23]
Attack Reduction fades from your Iron Starlette.”, – [24]
Round 5", – [25]
Burrow applied Underground to enemy Lapin.“, – [26]
Wind-Up applied Wind-Up to your Iron Starlette.”, – [27]
Toxic Smoke dealt 99 damage to enemy Lapin.“, – [28]
Round 6”, – [29]
Burrow dealt 519 damage to your Iron Starlette.“, – [30]
Underground fades from enemy Lapin.”, – [31]
Toxic Smoke dealt 99 damage to enemy Lapin.“, – [32]
Toxic Smoke fades from enemy team.”, – [33]
Round 7", – [34]
Flurry dealt 150 damage to your Iron Starlette.“, – [35]
Flurry dealt 150 damage to your Iron Starlette.”, – [36]
Your Iron Starlette died.“, – [37]
Adrenaline fades from enemy Lapin.”, – [38]
Round 7", – [39]
Pandaren Air Spirit is now your active pet.", – [40]
In your case, the damage pattern was
150+501+150+413+150 = 1364 and then the final hit was 150, exceeding the Starlette’s 1400
In my case, the damage pattern was
150+380+150+519+150 = 1349 and then the final hit was 150, exceeding the Starlette’s 1400
No debuffs. No magic numbers, like being brought exactly to zero by spme specific hit. No end-round damage weirdness, but in both your case and mine, the starlette was brought to zero and did not Failsafe by the second hit of Flurry.
In none of my other tests was my Starlette brought to zero by the second hit of Flurry.
Would need a larger sample of tests to be sure, but I suspect that’s the bug - something like “test for Failsafe after final hit”, but Flurry then goes on to second hit. Similar to previously excavated inconsistencies when something is killed by an end-of-round damage.
Also saw some funny stuff last night with BRD’s final boss’s failsafe. If I used Sunlight the boss never failsafed. Not sure if it was always like that. It’s been so long since I’ve been willing to go in there. 
Gee, that was some thorough testing. I appreciate the confirmation, I’d been wondering if I was doing something wrong.
Further testing on my part confirms those two flurry hits are key. If Starlette survives both, fight continues normally. Dying on first hit, Failsafe fires and Starlette rezzes. But if it dies on second hit, dies permanently.
Further suspicion of a bug is its timing; hadn’t ever seen this until last Tuesday’s maintenance upload.
No, you just misunderstand the way Flurry and some other multi-attacks. If failsafe kicks in on flurry’s first swipe it revives and flurry’s second or third smack kills it.
Your above example is a draw in player pvp. The toxic smoke was applied before failsafe kicked in.
It’s to reduce the animation time. It also looks like that is not a stock pet battle window so there’s a possibility of addon taint.
Major point I’d been trying to make, and what kicked off my starting this thread, is that something that had worked fine for at least a year suddenly started working differently last Tuesday. Always a clue that the Maintenance update either included a hidden change in how a pet ability worked or that it introduced a bug.
The screen grab I show is directly from the Pet Battle log which I’m fairly sure is unaffected by Rematch, the only add-on I use.
Apparently, issues with multi-hit abilities have been noted before with Haunt, where the Haunter won’t come back to life once the Haunt DoT expires:
Sounds like a game parsing issue then with it not running the order of attacks consistently. I’ll do my best to see if I can replicate it.
edit: pet pvp ques are not popping to test.
Today seems like Failsafe is back to working normally. Went into the Flurry attack with 189 health, died after second hit and rezzed with 280 hp. Does sound like a bug that is now fixed.
As someone who regularly runs daily pet WQs, never had any problems with Mechanicals and their Failsafe rez till the Tuesday, Sept. 14 maintenance. Since then it’s been erratic when getting hit with a multi-hit ability.
Fairly sure sign that something changed, could be intended but probably a bug.
Made a thread for it on the bug report forum:
Just as an aside, basically whenever anything that may seem weird or off happens in pet battles, it’s almost assuredly not a bug but simply how the rules in pet battles works. The only thing that may be weird is sometimes animations can be weird/misrepresented. But the core fundamental rules of pets and pet battles are solid and bug free and have been for years
Afraid I’ll have to disagree with you here.
Some background, most days I do various pet battles as a great way to level both pets and alts, and maybe pick up some pet charms. When I use exact same strategy I’ve used hundreds of times for over a year and it works differently, something must have changed.
First time it happens, oops, I must’ve done something wrong. But I check the Pet Battle Log and retry and exact same failure and it’s obvious something is different. When this happens just after a Tuesday maintenance and update, seems especially suspicious.
Well-known problem with software systems, even with those not as insanely complex as WoW, is how a simple change somewhere can affect other parts of the system that would seem totally unconnected. Whatever has happened, Failsafe works differently now, with different pet battles.
Follow the comments on Xu-Fu’s for a while. There are some people who don’t, or perhaps don’t even know that the Pet Battle Log exists.
There certainly are bugs. I don’t follow them closely, though others do, but they are mostly pretty long-standing and consistent in the way they present, especially end-of-round and death/resurrect bugs.
However, when I hear a report of an alleged bug or strategy failure from someone who is not presenting a log as evidence, I am inclined to caution, and assume PEBCAK as my default hypothesis.
