update: When I first go into Myth it works fine. If I watch a recorded show, at some point during the playback I lose functionality for those same keys. Exit (escape in Myth) is the worst, can't back out to previous menus. Also, with no "info" key (i in Myth) I cannot remove files. These may be a settings though, previous versions of Myth I could just back out with left arrow or get to the info pop-up by right arrow, this version just cycles between the show list and the episode box. Hitting the corresponding keys on the keyboard still work fine. If I exit Myth with the stop button and immediately go back in, everything works fine again.
Also, during playback of recorded video (and live TV) it occasionally pauses for anywhere from a few seconds to over a minute. During this time I cannot hit escape to back out, hit stop and get completely out of Myth, nothing. Just a momentary complete freeze of the MD. 3 (or was it 4?) times during the playback of a 1 hour show last night. It's very possible that the loss of functionality of certain keys on the remote starts when I get this pause, but I haven't tested this. This freeze does not happen during normal video playback, only in Myth.