Buffer corruption with jka-compr.el and revert-buffer

In GNU Emacs 21.3.2 and XEmacs 21.4.12 (and lots of earlier versions of each, apparently, such as GNU Emacs 20.7), put the following code into jka-compr-revert-bug.el: --------8<---------8<-------- CUT HERE --------8<---------8<-------- (shell-command "echo 'aaa' | gzip > /tmp/aa.gz") (shell-command "echo 'b' | gzip > /tmp/b.gz") (auto-compression-mode 1) (find-file "/tmp/aa.gz") (shell-command "cp /tmp/b.gz /tmp/aa.gz") (revert-buffer t t) --------8<---------8<-------- CUT HERE --------8<---------8<-------- Now do: (x)emacs -q --no-site-file -l jka-compr-revert-bug.el You probably have a buffer that looks like --------8<---------8<-------- CUT HERE --------8<---------8<-------- b a --------8<---------8<-------- CUT HERE --------8<---------8<-------- Yikes! It should just contain a 'b'! This only seems to happen if the original file is at least 2 characters longer than the new file. The underlying file is not changed but, when you edit and save, the corruption obviously makes its way into the saved file. I've had a look at revert-buffer and nothing jumps out. I've also had a look at jka-compr.el and I've run away screaming... I suspect it would be a lot simpler without all that coding system stuff... :-) peace & happiness, martin