Well, yes, as long as a software-list entry is selected and the software-list detail is the active one, QMC2 will stubbornly launch the emulator with the selected software's parts mounted -- unless you change the mount options (see below), switch to a different detail or change the machine itself (which will clear the software selection). There's no need for a new device setup, though.

If you want to avoid a software's parts being mounted, you can expand the software entry (click the arrow or + symbol in front of the selected entry to expand the tree), then select "don't mount" on one of the parts (all should switch to "don't mount" at once when there are multiple parts).

A mind is like a parachute. It doesn't work unless it's open. [Frank Zappa]