When you open a Piano Roll View that contains a drum map, the left pane (i.e. the Note Map pane) is always too narrow and slightly scrolled downwards with a blank area at the top. Of course you can easily adjust it but it doesn't remain the way you set it and reverts every time you close and re-open PRV (or change screensets).
Apparently this bug has been present since Sonar 5 and has been reported more than once. Here is an old thread from 2007-2008 discussing the problem:
http://forum.cakewalk.com/m981803.aspx This year I upgraded from v7 to X2a and was surprised to see the same behaviour still present. Unless it has already been fixed in X3d, then Alex may wish to add this item to his list of outstanding issues.