I spent 2 hours working on this before I discovered the extremely subtle relationship between EXIT, ONEXIT, a persistent script and #InstallkeybdHook. I read ALL the documentation about each. thoroughly. The DEWD did point me in the right direction to understanding the issue. (However, I DID READ that quote and believed that my code should have made my Exitapp execute.)
Yes, this is not a bug. and should be moved out of the bug forum. That is not to say, however, that I should not have posted the issue. I must also add that I searched both the old and new AHK forums for help on this issue. I found NOTHING even similar to my problem. Having used AHK for about 7 years now, I usually find that my difficulty in understanding comes from the difficulty of wading through the documentation. I feel this is entirely about the idiosyncratic way EXIT works in this context, and just wish there had been one small note about that.
Thank you for you input DEWD. As to the other respondent, I think you were just wasting your time being condescending.