JP1 Remotes

FAV is defined as part of the Sony TV upgrade installed in my 10820 and it seems
to work fine (i.e. it sends the Sony FAV command which the TV responds to).

FAV is not defined in any other upgraded installed on the remote, nor does it appears
in any macros. However, if some device other then the TV is selected and the FAV
key is pressed by accident, then the LED blink randomly and the remote crashes.

Ideally shouldn't a unmapped key which doesn't correspond to a macro or keymove simply
be ignored?

Well ... I should have done a better search on the board before posting.
As was pointed out this is a known problem and the work around is to
bind a NOP macro to the FAV key. I bound X_TV;X_CANCEL to FAV and
the problem went away.