MissionPlanner is deleting signing keys randomly

For the last few MissionPlanner versions, it's always deleting all saved signing keys randomly (withing few times of opening/closing).
It's so annoying because I have to add them all the time.
Adding immutable flag to authkeys.xml file causes MissionPlanner to be unhappy. Does it really keep it open in writable mode? Or switch to open as writable when it needs to save a new key? Maybe it's simply corrupting ?

Start by reproducing the repeated MissionPlanner open/close cycle and inspect how authkeys.xml is read and written. Trace the signing-key persistence path to determine when saved keys are removed or the file is corrupted; done means existing signing keys survive normal application restarts while new keys can still be saved.

Written by the indexing model from the issue text.