[Zope] BBEdit irritation

When editing zope source with BBEdit (on OSX), every time I switch to the browser(to see the changes I've made) and return to BBEdit, BBEdit thinks the file is un-editable. I hit a key, a dialog pops up, saying the file might or might not be editable, I carry on and everything works. Is this something to do with aquired permissions? any ideas anyone? tom