I think you mean if Sinclair uses Vindicta's ult, then the bug happens.
I've also reproduced this yesterday. It seems that:
If you use all charges your ult goes on cooldown and returns to Audience Participation as normal, although I'm not convinced the duration is being calculated properly. I might just be ignorant of how long half of Vindicta's cooldown is, though.
If you use a charge and have multiple charges unlocked, then the expiry timer vanishes and you can even gain more charges over time. As long as you don't fire the last charge you get to keep her ult forever.
