I was trail running and hit the lap button on the watch. The lap screen appeared and froze - the watch was unresponsive, except for a restart, which I performed. After restarting the watch, it continued on from the point at which it had frozen before (so the run was preserved). This is the first time I've had this occur, and the only thing I was doing that is not normal for me, is to use the music controls on the watch. I was also navigating a course at the time and using livetrack. I'd be curious if anyone else has seen this behavior. I reported it to Garmin support, but I'm not sure what happened to my report after that.
Note, I frequently use the lap button to mark an area on a course that I need to fix TBT for.