403 HTTP error caused by the text "print(" in a post

Attempting to Preview or Submit a post containing the text "print(" without the quotes, causes a "403 Forbidden" HTTP error.

A member of our forum triggered this when trying to post some code between [code]...[/code] tags. I narrowed it down to this minimal string, and then found that it didn't need to be between [code]...[/code] to cause the problem.  The problem does not occur with "rint(" or "print". It also occurs when there is a space between "print" and "(", i.e. "print (".