wow, that is so odd. umm, then I would say look into what Mastic_Warrior said. I know that there is a command you can run to set defaults in the terminal, I don’t know if it works the exactly the same on ubuntu as it does on debian, but might help. I would also look at the advanced settings of your DE maybe it is locking the program, like Dconf-editor or something.
terminal command to set defaults was this