That's really weird. The wheels should have no effect, because its the overall tire diameter/circumference that will mess up the transfer case. The difference between those two sizes are within tolerances front to back.
Anyway, I was on 19x9.5 et45 and 19x10 et38 when I ran them. They were smooth as butter. Then I just put the same 275/40's on the 9.5 fronts before picking up 2 extra 10's. All option worked perfectly, so I really don't know what to tell you.
only thing I can think of (and it's a huge stretch) would be that you're rears were worn down very far while your fronts were new (causing enough of a size difference) or the tires had manufacturing defects of some kind...
I can guarantee that the staggered setup had zero problems with my transfer case. And I doubt there was any real difference between our model years that would relate to this issue (mine was a 2007 3.0si).. All that being said, I do like the 275/40R19's all around much better.
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