The title pretty much says it.
If you assign a bonus that drops your rep back below 50, you can't comment on anything (popup appears: "You need 50 rep to comment"). A nice reward for setting a large bonus.
I haven't tried to do anything else.
Perhaps the "rep" threshold for comments (and other actions?) should be "current rep plus sum of bonuses awarded"? This would probably apply to SO and other StackExchange sites, too.
That's the way bounties work. If it drops your reputation below the threshold for a privilege, you lose the privilege. You'd lose the same way if you lost the privilege for another reason (because some of your answers were unaccepted, because you received or cast downvotes, because some of your posts were deleted, etc.).
There's been discussion about this ever since the Stack Overflow days. There's a feature request to exclude bounties from affecting privileges, it didn't get much traction. There's an open feature request to notify users that the bounty will result in losing a privilege.
