Emacs version is Aquamacs/Cocoa, development build (dr/dev branch), based on current Emacs 23 in development (which is probably sufficient to reproduce). This occurred during redisplay, more precisely when scrolling down with the mouse scroll wheel. (window-start) after the scroll action is 6150. SLIME is some recent CVS build. lispdoc.lisp is attached. Warning (slime): "lispdoc.lisp":166:0 (pt=6683). Caught error when trying to extend the region for fontification. The error was: (error "Invalid search bound (wrong side of point)") Further: font-lock-beg=7694, font-lock-end=8223. This is a bug in Slime itself. Please report this to the mailinglist slime-devel@common-lisp.net and include your Emacs version, the guilty Lisp source file, the header of this message, and the following backtrace. Backtrace: backtrace() (let ((standard-output standard-output)) (backtrace)) (progn (let (...) (backtrace)) (with-current-buffer standard-output (buffer-string))) (unwind-protect (progn (let ... ...) (with-current-buffer standard- output ...)) (kill-buffer standard-output)) (let ((standard-output ...)) (unwind-protect (progn ... ...) (kill- buffer standard-output))) (with-output-to-string (backtrace)) (slime-display-warning "%S:%d:%d (pt=%d). %s This is a bug in Slime itself. Please report this to the mailinglist slime-devel@common-lisp.net and include your Emacs version, the guilty Lisp source file, the header of this message, and the following backtrace. Backtrace: %s -------------------------------------------------------------- " (buffer-name) (line-number-at-pos) (current-column) (point) (apply (function format) message args) (with-output-to-string (backtrace))) slime-bug("Caught error when trying to extend the region for fontification. The error was: %S Further: font-lock-beg=%d, font-lock-end=%d." (error "Invalid search bound (wrong side of point)") 7694 8223) slime-extend-region-for-font-lock() font-lock-default-fontify-region(7694 8223 nil) font-lock-fontify-region(7694 8223) run-hook-with-args(font-lock-fontify-region 7694 8223) byte-code("\302\303 #\207" [start next run-hook-with-args jit-lock- functions] 4) jit-lock-fontify-now(7694 8194) jit-lock-function(7694) --------------------------------------------------------------