Stop using the gui and open the .desktop files as they were meant to be, with a command line editor. Then this won't happen.
Also it would do you well, considering your posts today, to look at the if you are new to bt and or linux thread linked below.
See also this search string
change default open with ubuntu - Google Search
And here:
Unable to change default program from Open With tab - Ubuntu Forums
Those may provide more help.




