Hi Kieron
It sounds to me that your issues all relate to what Jill has referred to.
I wouldn’t try to get your new projects to automatically open in the version 11 betas. Instead, start Pte11 beta then use File Open to start them.
Also, each time you install a fresh beta version, make sure that the box which Jill refers to remains unticked. That should ensure that double clicking a file will still open it in Pte10.
Sorry Jill, for basically repeating what you have said, but I feel sure that you are right.
Regards
wideangle