I just submitted a bounty on a question and I typed a custom reason. Here is what I saw:
I know that I typed the bounty message correctly, because it displays properly in the actual question. This is only a problem with the display of the bounty message submission box. I am using Firefox 24.0. Notice that not only is what I've typed corrupted, but also the leftmost characters in the number of characters remaining and the Enter a custom... header and the Are you sure... message and the Back button are also cut off.