On classic client only if you grab a mounts health bar, either your own or another player's mount, and that mount then gets mounted, you will then lose that health bar.
Both clients, if you grab a players health bar and that player then leaves the server or logs out, the name on the health bar will change to a duplicate name of another players health bar that you have.
When this thread first appeared I posted this bug as it was the general consensus among my team that this was the most annoying. Since March 28th 2012 when this was posted we've seen little development. I perhaps should explain why this bug is annoying for those devs who have never actually played uo. Since they clearly bypassed it in order to spend more time doing pixel candy for us.
When you grab your 10 friends' health bars, and half of them have moved out of sight, half of the 10 health bars will read 'John Smith', say your friend Pjay has changed character or simply logged out or you no longer wish to have his health bar because you're fed up of healing him, you need to then close that inactive player's health bar (since for some reason you can actually only have 10 health bars and space is now precious) however you don't know which is the inactive player since half of the bars all read 'John Smith'.
Now everytime someone logs out or changes char, you need to then regroup everyone and grab bars again, rince and repeat.
As for the mount healthbar problem, this is as bad as an exploit, I can continually mount and dismount my dreadmare while chasing someone and they're unable to paralize it without having to grab it's bar everytime i mount and dismount it, sure they can use last target, but then that doesn't help them when they are trying to target me also.
