On my Emacs (Aquamacs on OSX, latest version) the command Edit -> Spelling -> Mark All Misspellings goes through the whole file (from 0% to 100%) and then starts again at 0%, and continues ad infinitum.
The menu item runs the command flyspell-buffer (found in global-map), which is an interactive autoloaded compiled Lisp function in ‘flyspell.el’.
I cannot do anything else and have to abort Emacs to stop the command. What am I doing wrong?