@theluthier I'm wondering why "Join as UVs" didn't work on your model. On my model, this operation was successfull. You explained the problem with a possibly wrong vertex order. Couldn't this be solved by recalculating that order?
I've joined the claws again in one mesh and the 4 UV islands align perfectly.
Forwarding to this thread of the same subject: https://cgcookie.com/questions/13068-why-do-some-claw-toes-have-distorted-textures-despite-having-identically-looking-uv-map-islands-as-claw-toes-with-undistorted-textures