Something in the back of my head says that Mb Z-axis and Maya Z-axis aren't the same. In fact, doesn't exporting Mb to Maya involve a subsequent rotation of -90x 180y to get into the proper orientation? Now, I'm a couple of versions behind (ver5.5) so this might have changed, otherwise try unrolling that global rotation (180y +90x? my cartesian arithmetic sucks don't it?) first then export it.
Good Luck, as this is an old post I imagine you solved it already.
T.