Can't unmount volume because of Deskbar add-ons

[donn]

When ProcessControl et al. are not found on the boot volume, Deskbar may start them from other volumes as found by fs query. Any such other volume then can't be unmounted, because it's running one of those add-ons.

I wonder if the use of a query here is itself a bug. What if the query finds an old, incompatible or otherwise broken file? When I have old system/apps/ directories laying around from previous releases, can we guarantee that the query will prioritize /boot/system/apps/ProcessController over other ProcessController instances that may be found in random locations on the boot volume?

(running hrev34766.)