I had my XH in the air swapping wheels around yesterday, spun both axles and each time noticed that the other didn't even twitch. Driveshaft spun, so I'm pretty sure it's not broken, but my understanding is that an LS diff will spin both the same way, and a single spinner will spin in opposite directions. Diff makes no noises, everything operates smoothly etc, it's just that neither wheel seems to be connected to the other. It's... odd, to say the least
Anyone have an idea of what could be going on?

An LS diff will (should) spin both wheels. If you hold one wheel and attempt to spin the other, a heavy resistance will be felt, almost to the point of not being able to turn the wheel, the power being directed to the wheel with least resistance.

An "open" diff will only spin one wheel, the one with least resistance. If you hold one wheel, the other
will spin quite freely. Letting both spin, they may spin in opposite directions, but this is not important.

If you have an LS diff in, it will (should) have a sticker on it saying so. If there is no sticker, you have an "open" diff.

No, thats not right JoshXH.
An open diff WILL spin the other wheel the opposite direction if theyre both jacked up off the ground. There are some really good videos on youtube that explain it.

creeture3, not sure whats going on with your diff. Is it an LSD? Should be stamped on the diff.

Both wheels were in the air, probably should have mentioned that. I know how they work, but the lack of any movement at all from the opposite wheel to the one I was turning threw me, lol
It's a moot point now anyway, I've got a complete disc-to-disc LSD out of a V8 ED wagon to pick up when I get my tax back. Should hopefully fix the big P-plater Commonwhore spec whiparounds I was getting in the motorkhana up at Monkerai B&S on the weekend, lol