I see no distortion on windoze. Rotated and grabbed bones without doing anything but toggle from Ortho to Perspective. But I see that you have both Vertex Groups assigned to both Cubes.
if you’re able to rotate one cube at a time then I have only one vertex group assigned to one bone. If I had both vertex groups assigned to both bones… you’d get deformation too. Even if I delete the other vertex group from a bone … I still get deformation… in any case, it works for you but not for me on OS X
I noticed that you help a lot of people on this forum and not everyone seems appreciative… I just wanted to let you know I’m glad you’re here and thank you for all your help.