Rigging IK strange mirror problem

Hi, im new in the forum, i just try to make low poly models of my characters so i can get his proportions right.
Problem is that after i make the rig and complete de IK settings, i try to move an arm or a leg, and his counterpart in the other side of the mesh, gets all messed up-
The mesh is not associated to rig beyond the automatic weights.
Please help u.u