This is probably a non essential feature but useful none the less..
In the image you will see my disc type pane, circled in red as well as two highlighted entries, "Album" & "Ep" I managed to select both Album & Ep in the pane by holding down the Ctrl key as I clicked.. I'd never tried this before today but it works
and seems like it could be quite useful (Probably more so on my smartlist panes, or artist panes rather than disc type")
Where it says disc type in the image, if that were a left click able button, that would enable
"sticky" selections for that pane, it would make it a lot easier as well as it would give people two ways two make sticky selections. (It would also make the sticky selection feature more accessible to people who less enabled to make a sticky selection in the first place, i.e. someone who has lost an arm..)
You'd probably have to place a marking, in the right corner of the top of the pane to indicate that it is button. Also raised when selected and vice versa when not..