You were right. What finally happened is that we found out the tilers
had done a 5-point mortar installation, meaning they put a thin layer
of mortar on top of the cork, but really only had the tile cemented to
the floor at the corners and the center of the tile. The Acousticork
company AND the tile assocation of america both said that was NOT going
to work, especially over cork. So the tilers removed everything (the
upside of the bad installation was that they were able to easily remove
the tiles without breaking them) and retiled it all the normal,
mortar-everywhere way, as well as putting epoxy grout in which
acousticork said was necessary. Aside from being out of our condo for
2 months, we're very happy with the way it turned out now.