According to the http standard, URL's with spaces in them are invalid. You never used to see URL's with spaces in them on the Internet until IE introduced the "feature" of automatically re-writing URL spaces at %20.

Netscape 6.x series and Mozilla both re-write URL's to include the %20 in place of spaces as well.

Isn't this BBS software written using PHP? If so, it should be simple to make it put a %20 in place of all spaces. A few months back I modified the Ultimate Bulliten Board code used on nsxprime.com to fix this very problem-- only took one line of code to fix.