Deleting a file in Zerberus doesn't work

On Xubuntu 14.10 (MuseScore commit 5f30234), add a SFZ file in the synthesizer Zerberus, click "Set as Default", close MuseScore and open it again. The synthesizer will automatically load the file. No bug for now. All is fine when adding SFZ files, but there are two bugs about deleting them:

1. Delete the file in Zerberus, click "Set as Default", close MuseScore and open it again. Bug: the file is still loaded. Note: Fluid doesn't have this bug. Deleted items are not loaded again.
2. Delete the file in Zerberus and open the mixer. Bug: instruments of the SFZ file are still listed. Note: Fluid doesn't have this bug. If we delete a SoundFont, its instruments are no longer displayed in the mixer.