Animations will not end at the correct time.
I don't even buy demo charges when doing a fed anymore because I risk a 50% chance that once the channel ability is completed, my character's animation will not end and I'll just be standing still next to the door where the grenade at, casually still in the "planting" animation, before blowing up since I can't run away.
This problem has also been known to occur when finishing revives, cancelling revives, or cancelling hacks/ demos. Repairs and bloodbags are somewhat more reliable, so I'm not sure what's different about those.
EDIT: Also, I'm considering the fact that the server doesn't tell you when somebody logs into a rebel a fucking bug. It's so aids to completely sweep a rebel top to bottom only to have someone log in directly behind you while you're buying gear with no indication.