21.2.32: Error caught in `font-lock-pre-idle-hook'

After upgrading to beta32, forwarding large mail messages in Gnus with `S o m' gives me the following errors before giving up: (backtrace attached below) (219) (error/warning) Error in `pre-idle-hook' (setting hook to nil): (error Lisp nesting exceeds `max-lisp-eval-depth') (220) (error/warning) error: (error Lisp nesting exceeds `max-lisp-eval-depth') (221) (error/warning) error: (error Lisp nesting exceeds `max-lisp-eval-depth') (222) (error/warning) error: (error Lisp nesting exceeds `max-lisp-eval-depth') (223) (error/warning) error: (error Lisp nesting exceeds `max-lisp-eval-depth') (224) (error/warning) error: (error Lisp nesting exceeds `max-lisp-eval-depth') (225) (warning/warning) Error caught in `font-lock-pre-idle-hook' Before bombing out, the "Fontifying *mail* ..." buffer seems to take exceptionally long to finish.