Strange Drum Editor Bug

[lloydcole]

When I am editing within the drum editor, moving notes, copying etc - I am getting notes automatically deleted from the beats just beyond those that I can see in the window - eg I can see bars 3-5, notes are deleted, always from a single beat - at bar 6 beat 1.. I do not know when they are deleted because I can't see/hear they are missing until I play the song.

I have created a clipping of the drum MIDI and started a new file from scratch, but the problem still occurs.

I opened another file that I couldn't recall having this problem with and could not reproduce it there.

Using DP 4.5, OS10.3.8, which had been pretty solid until now.

I'm guessing there is something corrupted in the file, but one would have thought starting afresh and importing clipping would have fixed that..

Any help would be appreciated. MOTU tech support have drawn a blank, so far.