Recently, I upgraded my Google Calendar resource, to solve sync problems. The Calendar resource was upgraded, but the Tasks resource was superceded by the new Tasks handling in the Calendar resource. And I was stuck with 2 Tasks resources: one, stuck in time, and the other, current. When the Akonadi agent associated with the Tasks resource disappeared, Akonadi couldn't remove the resource anymore. I had to invalidate the resource using Akonadi Console, but Akonadi Console can't remove properly the resource, so I'm left with a ghost Tasks folder, that doesn't do anything. Akonadi MUST gain the ability to remove resources on its own.
I get the same problems with resources created by the external akonadi-google plugin which aren't reused by the resources created with the new kdepim 4.9.
Updating version and status.
This bug has only been reported for versions older than KDEPIM 4.14 (at most akonadi-1.3). Can anyone tell if this bug still present? If noone confirms this bug for a recent version of akonadi (part of KDE Applications 15.08 or later), it gets closed in about three months.
Just as announced in my last comment, I close this bug. If you encounter it again in a recent version (at least 5.0 aka 15.08), please open a new one unless it already exists. Thank you for all your input.