Potlatch3: newly added Background Imagery entry is not saved

[BikePC]

When I add a new Background Imagery entry (Background - Edit - Add) the new entry works nicely during the current session.
However after starting a new session of Potlatch3 the entry has been disappeared and has to be added again every time.

My question: is there a way to keep newly added entries in the list for every new P3 session? Is there a local file which can be edited?