Robotics do not behave equally.
Just take any robotic part and place it in symmetry. Mirror or radial, it doesn't matter. These parts are not behaving equally, one of the parts is almost always behaves weaker than the other, even if it's locked. Just watch the attached videos, you will know what I mean.
UPD. Sometimes they both behave weak: https://youtu.be/pIh35JQxcGc
UPD 2. It looks like even symmetry has nothing to do with it. I just tested it without a symmetry at all, individually placing robotic parts, and it still does it.