I've done a little more testing with regard to my Asus netbook and build 41 mouse issues. I mainly work in the 'panes' screen with panes for 'artist' and 'album'. Something strange has emerged, related to the netbook's mouse system.
The machine has, in addition to physical left and right mouse buttons, the ability to double tap the touch-pad which simulates a left button double click (this functionality being dependent on a driver supplied by Asus). Until today, I have never noticed any distinction between a double click generated by one method or the other.
Double clicking the physical left button, all is well with build 41. Double tapping the pad, however, works correctly when the mouse is pointing at a song title, but not when pointing at an album or artist! The 'double click' instigated by this method is effectively ignored by Media Center. I've tried enough times to be, say, 95% certain about this.
Hopefully, this information will make something click(!) in Matt's mind.