Contrary to its name and all the documentation I have read,

append-next-kill sometimes causes the next kill to be prepended. Example

(in emacs -Q): Type "foo bar", then C-a M-d C- C-e C-M-w C-w C-y. The

yank produces " barfoo". This command would be much more useful if I

understood when the next kill appends and when it prepends.