I would like to put this here:
When I use an ability that makes me unstoppable, I do get my 50 Mana back, however, should I use this ability against within 5 seconds, this does not restore 50 Mana. Please remove this internal lockout from the item, thank you.
no, it works different from what you said. It only grants mana when you gain unstopable. for example, if me, druid, use Earthen Bulwark, gaining Unstoppable status for 3 seconds, if i use anything else that grants unstoppable that will enlegthen my unstoppable timer then i wont get 50 more resource. However if i just wait until my 3 sec unstoppable ends and then get another, i will get resource 2 times.
By the way, it works with aspect of metamorphosis.
Use unstoppables with lower timers.
We had this discussion in s2 I think,
The longer unstoppable skills or aspects that make them longer do not work well with Tibault’s will.
My Ice Armour, Flameshield and Teleport grants me unstoppable, why is it then, that when I use it with one ability, it works fine, but subsequent abilities that grant them, do not, only after 5 seconds do they once again restore the primary resource.
It is you sir/madam, that do not grasp how this idiotic item works or how it SHOULD work I should rather say.
they actually explained it to you. you need unstoppable to fully run out and use the next unstoppable skill for it to grant ressource.
one of the reasons why people in s2 made new characters in s2 and didnt level up metamorphis to reduce its unstoppable duration.
especially on sorc its pretty easy to just -stay- unstoppable. make sure the buff runs out if you are mana starved.
“When you become Unstoppable, gain 50% of your primary resource”
English isn’t my primary language, as some of you have decerned, Hower, the top text to means to me, it shouldn’t matter how many times I become unstoppable, this is what SHOULD happen.
When the buff refreshes, you can see you are still unstoppable when you activated a new ability that grants it, however, you can no longer have a visual aid to help track the internal CD of when you are going to get the mana, the buff overlaps, do you get it? It’s annoying, when you need every drop of mana for CD’s in high risk scenarious, this idiocy is the last thing one has to keep track of.
You can’t gain unstoppable if you’re currently unstoppable. Wait for the chain icon above your head to go away before using next unstoppable skill.
oh im with you on the “tracking buffs” part. I also wish there were ways to adjust the buffs you want, or need to keep track off really.
also, your english seems fine =)
you became unstoppable once. you then use other abilities that only lengthened your unstoppable. you never stopped being unstoppable. in order to get the mana again you have to stop being unstoppable and then use an ability and you will then become unstoppable again
Why doesnt it just refresh the unstoppable, like almost every other skill in the game? Why does this specific ability have to run out to work again?
Now I really want a rework. 
there are actually quite a lot of buffs that work this way, especially on the paragon boards.
Which specific ones? And I’m not sure those buffs are orange to orange comparisons.
The tooltip says “when you become unstoppable” - this means, to me, even if you are already unstoppable, you “became” unstoppable again using a different skill.
i can do a list later i guess, one that instantly comes to mind for example is necromancers “flesh-eater”.
pretty much what lavawhisp said, one could interpret it your way i guess, but yea, infact you never stopped being unstoppable, hence why you are not “becoming” unstoppable, you just “stay” unstoppable.
let me make a comparison to see if we can agree.
I use Aspect of concentration in my build. it grants me 20% damage reduction each time I cast a conjuration skill for 5 seconds. I use hydra in my build-and usually spam them to retain my 20% DR. Does this mean that my prior 5 seconds of protection has to run out for the ability to work again? I would surely hope that is not the case, as that wouldn’t make much sense to me. I could be on second 4, cast it thinking I have 5 more seconds, and only really have 1 second of DR.
you are right on this one, thats not the case there, as all the conjurations you summon are seperate instances. Hence why it says “each time you cast”. Thats not the case for tibaults - it doesnt say “each time you use a skill that makes you unstoppable…” it just says “when you become unstoppable”
how is that different
What is the difference?
as pointed out, the difference is that in the case of “when you become unstoppable”, it needs you to be stoppable in the first place - whereas if it said “every time you use a skill that”, it wouldnt need you to be stoppable in the first place, it just needs a skill that would have the potential to make you unstoppable.
not sure if that saying works in english, but in germany we say “the devil is in the details” 
no because like you said you gain it on conjuration skill cast. you only gain the tibaults buff when you become unstoppable. you dont become unstoppable if you are already unstoppable
Bad example for “become unstoppable”. Although good example for keeping the unstoppable duration up similar to the DR, it refreshes the duration but since you didn’t lose the unstoppable effect, the pants don’t give resource.