Blender Armature / rig is getting random rotation values (not the Z problem)

Hi,

We're working on a game that requires us to rig the characters on a 2D plane (Z rotation only). However when we import rigged models from Blender the bones seem to get strange random rotation values on the X and Y axis (like 1.3523523 or other strange random values). The original blender file shows that everything is correct and only the Z axis is rotated (X and Y are always 0). This is messing up with our rigid body configuration.

I am aware that blender switches the Z as the Y axis. If this was the case we could solve this easily. However it doesn't seem like it.

Nothing we do seems to change this. It happens on multiple characters and we tried re-rigging them several times using different techniques. It seems to be something in the import. This appears to be completely random without any real pattern. From time to time some bones also show up as 0.999999... scale. We don't touch scaling and we're sure of it.

We tried using both .FBX and .blend files. Both show up the same results. We also tested this with both Unity4 and Unity3 (we thought maybe it's a new bug).

Any ideas? We've been hitting our heads against the wall with this for a few days now.

Thanks!