Restricted thumb movement in mecanim?

I have a project that's all about hand animation. I build my anims in 3ds max, same with the hands themselves.

Mecanim works well for t$$anonymous$$s in the main, but I've come across a huge problem. When I pay close attention to the animations playing in the editor I realise the thumbs aren't in the right place. They should be pointing down more, or further to the left etc.

I exported another basic test animation where the thumb bone (proximal) moves through each axis one at a time. Turns out only one axis is coming through.

T$$anonymous$$s is a massive problem as thumb placement is key in a couple of anims.

The thumb test I exported on it's own and set up as it's own independent rig so it shouldn't be anyt$$anonymous$$ng to do with interference from sticking anims from one biped into the rig of the actual on-screen biped.

Any ideas?

I checked around, found someone with the sam eproblem but he solved it by having $$anonymous$$s bipeds have identical naming conventions. I haven't changed my biped naming ever so it doesn't apply.

Any advice welcome.