This issue appears to have been fixed in the latest CVS code.

If you are able to test mantis on a development box, then you may like to try a recent CVS snapshot from http://www.mantisbt.org/cvs.php and see if this resolves your issue.

NOTE: the CVS snapshots are unstable releases, and should not be used in production, and you should wait for the next release of mantis to resolve this issue.

Thank you for the report