I am on Windows, 1.10.5.1342. I just now checked to make sure it was on 80, then closed the program, opened it, loaded an image, went to file>export, and it is set to 100 so it is not remembering.
I cleared my prefs as you suggested and have the same result. Closing the program causes it to forget the quality setting of 80 that I put in the JPEG export settings box.
Unless I am missing something (entirely possible), to export from photo persona it is File>Export. If I want to do the same thing in the export persona it is Export Persona>File>Export so an additional step. Besides, the way I am doing it SHOULD work it sounds like.