Perhaps people already knew this, but I didn't: detaching from the project kills any phantom models at the server.

A Windows machine of mine had five phantom ANZ models (i.e. appearing on Web pages but never downloaded). I thought that these would hang around until the deadline expired and then be reissued, rather too late to be of any use. Having run a few HADCM3S to see if they worked, I detached from and then reattached to the project to clear up the HADCM3S debris. The phantom ANZ models are now marked as "client detached" and have been reissued for other crunchers to process (e.g. hadam3p_anz_rrdn_2012_1_008962062_1). Well done BOINC.

I think it's the 're-attach' step which is crucial here. If you simply detach from the project, the server doesn't get any message to say you've gone. But re-attaching makes BOINC check the consistency of its database.