currently it will say a url is invalid given something like
td://nafs.nafs.qualitycenter/qcbin/Defects?Action=FindDefect&DefectID=9549

in this situation http://forums.atlassian.com/thread.jspa?messageID=257291048&tstart=0#257291048 , the user knows that all users will have browsers compatible with td://

so, either make it easier to modify the validation, or as Niels suggests, add a "i know what im doing, trust me" checkbox.