signing a petition results in duplicate records being created

Campaign/Form/Petition/Signature.php seems to try to run the default dedupe rule. However, it passed the variable $this->_ctype to tell the dedupe rule what contact type should be checked.

However, it seems as thought $_ctype is never set.

I think it should come from the Contact profile used by the survey.

If this sounds like I'm on the right track- let me know and I can try to work out a patch.