I had considered the problem with a merge, since I did merge one side of the family tree with another early on, but, again, why would those relationships appear as grandparents in 2009, but not 2010?
Of course, I've looked at the Relationship Tab in the People Workspace. Can't find anything out of the ordinary there either.
The parentage and marriage reports showed up the same information on relationships as well.
As for data error reports, I had the usual data errors such as "Missing Marriage
Date" or "Birth date missing" etc. It took me an entire day just to get through all reported data errors for 15,000 people!
I'm at a loss, completely. The only logical thing I can come up with (other than the obvious limited configurations from the developers) is that there was a huge quirky problem when I uploaded from 2009 to 2010. And yes, I uploaded entirely new files in two different ways, GEDCOM and FTM, just to try and get a logical relationship.
However, if I go to the Relationship Calculator, the "preferred" logical relationship can be chosen from the drop-down menu, but it reverts back to the crazy relationship when closing the calculator.