In the entry pane, some of the information I have entered in one tab is lost after I switch to a new tab and then return to the original tab. This is a pretty big problem, because I have to frequently reenter data. I hope you can fix this in the next release (I am using JabRef 2.9.2 on Windows 7).
Note that if I save the bibtex file, then I don't lose information after switching tabs, but the requirement to save before switching is at best, undocumented. And I keep forgetting to do this anyway.
"entry pane": what I see when I double click on a reference, the window that has "required fields", "optional fields," etc.
"some of the information": the most commonly lost information is the bibtex cite key, the title, and anything I've written in the review tab (this is the worst problem, because this can be a page or more of writing).
Which JRE are you using? Please try the most recent beta to check whether the issue also appears there.
Sorry to be slow in replying; by the time I got to this, I had already updated my JRE for other reasons. Now I'm using Java 7 Update 45, and don't see this, so it might very well have been a JRE problem.