I have the AcousticBrainz plugins loaded which create a LOT of webservice calls.

If I delete the album whilst these webservice calls are still queued, then the webservice calls are NOT deleted.

I am guessing (because I haven't had the time to review the code) that Picard does not associate a queued webservice call with an album or track object, and so is unable to delete these webservice calls from the queue when the associated object is deleted.