While I see why you want this, I'd prefer it'd stay as is, because its just part of the way the game is played, feel like this would unfairly deny opportunities for Ts to do their thing, which, contrary to belief of many, is the whole point.
Edit:
I highly doubt that it will only be used for CTs like others below mention, unless specifically coded to do so.
Also, why invalidate damage done to CTs by nullifying it with this kinda marker, if it were implemented only for CTs, again it is part of the point that, like t's, that they have to go to the health station to replenish. How is it fair to the Ts that the damage they put in for their teams is instantly invalidated? It'd defeat the purpose of rebelling entirely, because unless you have a gun or can get close enough to bomb, Ts would have nothing to keep CTs on their toes for, because any nade/molly would be pointless if it doesn't kill them.
It's a decent suggestion and thank you for suggesting it, and of course I'm just one person's opinion, I just don't see a way this doesn't disrupt the whole concept of JB, no matter how it'd be configured.