Xemacs warning message
 

I use Xemacs, when working with the file it splits window on two parts.

And shows the message on second buffer:"
(45) (warning/warning) Error caught in `font-lock-pre-idle-hook': (error No match 1 in highlight (1 font-lock-constant-face nil nil))".

I can close the buffer, but it happens often. Any ideas how to fix the bug?