I think all filters in all lenses should be multi-selectable. But it should be made consistent with all IconView-ish widgets in browse mode. That is, only select one icon at a time when left-clicking, but enable the user to select more by pressing ctrl or shift.
In this case, since there's no actions to perform, I think left clicking should select only one, but middle-clicking should add to the selection, and right-clicking should remove form it. That should make the GUI both more consistent with other software, and more comfortable when using a mouse.
I think all filters in all lenses should be multi-selectable. But it should be made consistent with all IconView-ish widgets in browse mode. That is, only select one icon at a time when left-clicking, but enable the user to select more by pressing ctrl or shift.
In this case, since there's no actions to perform, I think left clicking should select only one, but middle-clicking should add to the selection, and right-clicking should remove form it. That should make the GUI both more consistent with other software, and more comfortable when using a mouse.