Does anyone else have this problem or is my Delphi cursed somehow?

I'll have a bunch of forms and files open in tabs in the editor and I'll be typing away and then suddenly everything stops - my .pas file has, seemingly at random, become read-only.

Sometimes I can just right-click the tab at the top and uncheck "Read-Only" and continue, but sometimes this option is checked and greyed-out (disabled), meaning I can't uncheck it and I can't make any further edits to the file. This too seems to be random.

In the latter case, the only solution is to save the file in question, which works, despite Delphi's assertion that the file is read-only, close its tab in the editor, and re-open it. Not catastrophic, really, but it's starting to become annoying.

Could it be that I am hitting a keyboard command combination accidentally to do this or is this a bug in Delphi?

I'm in Delphi 2010, Windows 7. Doubt it's anything to do with installed packages, but if anyone wants the list I'll generate it and attach it here.