I use Arial.
I have been unable to find an exact sequence of events that will trigger the problem; it happens often, but sporadically. In fact, I was just now able to replicate the problem, but then unable to do it again with the same sequence of inputs. *facepalm* Underline seems to "stick" more often than bold, and it usually occurs when the two are used together. I use Cmd-_ shortcuts almost exclusively while typing, though, as mentioned earlier, when the problem does crop up, even clicking will not pull me out of the issue.
Steps I used to recreate the problem:
1) Begin new line
2) Type regular text
3) Cmd-U/toggle on
4) Cmd-B/toggle on
5) Resume typing
6) Cmd-U/attempt to toggle off
7) Resume typing/continues to underline
It only happened once out of 6 tries to intentionally replicate though. Seems to happen more often when I don't want it to
I'm fine without a support ticket.... I'm already pretty quick at working around the issue, and I doubt that it's caused by any settings on my end. Just thought I'd try to do my part to help you guys because I use the program so much but don't have a premium account
Other potentially relevant info for your team *shrug*:
Snow Leopard 10.6.8