I really can't see how's possible you would get a perfect parking rating, and then require a reposition to start deboarding. Are you sure you really required a repositioning and not, for example, just a Couatl restart, without having to move ?
It's possible there might have been an error after the marshaller danced, which might have stopped the procedure, so we would need a log ( be sure log is enabled in the Troubleshooting section of the Settings ), made after this happens, so we can check what really happened.