I rigged a mesh human I'd made and it worked fine. I deleted the parenting and the armature modifier between the skeleton and human so I could edit the mesh more. While editing the human, I decided I'd change one side and mirror it to the other. I deleted one half and mirrored the changed half to where the one I'd just erased was. I connected the skeleton to the skin again, using automatic weights as I had the first time, however the weights were asymetrical. The right arm of the mesh works fine, but moving either arm on the skeleton causes the left arm of the mesh to freak out. Same goes for the legs.
So, how come the automatic weights got messed up? Why isn't it grabbing the skin symmetrically?