Agree on that this should not succeed feeling here.
PARSE is a complex operation in itself already and changing the rules during that operation is something that I would consider to be a feature that should not be allowed in software that is to be maintained (on par with the GOTO statement). When such a feature is needed perhaps it is better to test in two or more steps.
Someone should bring an awfully good case for this to be possible to the table for considering it to be allowed. I'd say if you do this, don't complain about unexpected results.