WoW Classic Era
Seems to be a thing, other rogue in groups also agree the crit % seems incredibly low with the improved talent and they just end up playing swords / hemo
I think it’s bugged and not working
I don’t believe it works in classic neither.
Improved ambush and Remorseless Attacks work fine though.
Definitely an issue with imp Backstab
Hm, it’s working fine for me on a Fresh realm. I can see the what roll is needed to crit for a given attack, and Backstab’s crit chance goes from 16.9% → 26.9% → 36.9% → 46.9% for each rank of Improved Backstab. 
Could you both post screenshots of your build? If you don’t have the trust level to directly post links, you can bracket them with ` marks to make copy/pasting easy, like so:
https://us.forums.blizzard.com/ - I put a ` on either side of the URL to make it nice and easy to copy.
Maybe it’s just a placebo effect, but I “fixed” mine by changing my spending the gold to respec into the same spec. I have a feeling that I had changed my spec when there was something wrong with it, and since then it has been fixed.
I unfortunately don’t really have the stats, because in raid, you’re usually so close to crit cap that you barely notice if 10% crit is missing, but in dungeons, it was very to notice the multiple high no crit streak (12 in a row), vs crit streak.
But it seems fine now. Maybe I’m just extremely unlucky lol
I definitely think there’s an issue with the talent.
The fact that forum thread generated so much traction plus it’s generated traffic from Google searches based on the issue shows something isn’t right
I am unsure how to do this. However, my build is 5/5 malice, 5/5 imp daggers and 3/3 imp backstab.
I’ve had 8 backstabs not crit in a row which is just insane when you’re sitting at 55% crit rating