I call BS as well. As soon as this rumor hit these forums a few of our captains went on a mission to get to the bottom of it. It turned out it was ONE incident of ONE new MSP -900 FO who didn't realize they were upside down for a day. When he was told, he was embarrassed. The whole issue has since been a lesson in how gossip can spread within a company and how quickly the crewroom talk makes it onto the internet.
Even during recurrent this rumor was brought up many times a day... the captain who was on the case from the start was getting pretty frustrated trying to set everyone straight. At this point the truth isn't even important anymore.