It looks like he has a braided line on one side and a rubber hose on the other, the calipers look different too one looks newish.

I don't recall if you mentioned that you replaced the rubber brake lines, but if there is 'resistance" when bleeding one caliper, I would suspect that the line has swollen internally and not allowing free flow of the fluid. This would cause your brake to not release very well.

Internal swelling of flexible lines is not uncommon

Calipers pistons get pushed out toward the disk by the hydraulic pressure. There is nothing really to pull them back. No springs like the drum brakes have.  The do move back however by the slight irregularity of the disk "wobbling" and ushing the pads back. It takes very little pad pressure to grip a disk against hand turning. Stiff seals can be enough to do it.

Concerning your question about only one disk being turned by the motor after a brake applcaition: It does not take much resistance on one side for the differental gears to come into play. What you are seeing is one wheel has more resistance than the other, like driving around a corner, and the torque being transferred to  he other side.

put the car on the ground off your stands, and drive it down the road and shake it down that way, not up in the air.

Are you putting power to the driveline while the suspension is at full droop? It will have difficulty with this.

Sounds like the caliper seals are not flexing the pistons back when pedal is released.
Are the calipers s/h? If s/h, they need stripping and new seal kits fitted.

Your calipers are on upside down not the discs. Yes it is normal for one wheel to turn if you put pressure on that wheel the other will turn it is just the differential doing its job.

Image Gallery

This is hopefully a shorter thread, but in actuality is a continuation of the recent thread about the rears brakes locking up.  As noted there now replaced Master Cylinder, Proportioning Valve, and new 5/8" rear brake cylinders.  I've put the all four wheels of the car up on stands.  Started the car, ran it through some gears and found that the front discs (7.5") were yet tight after applying the brake.  The pedal, by the way, felt like it had little play.    

I had to find again, this note by C. Heleker that indicated I had the discs upside down (i.e on the opposite sides):  "....... It is not unusual for them to be installed upside down. The bleed valve should be at the top. If it is at the bottom, you'll need to switch the calipers side to side."   I have no idea why I installed them incorrectly.  

This photo, disc before.    

This photo, disc after (this is a picture on another car, but the bleed valve is now up, on the PUP):

So, now another test on stands, start up, put thru gears and hit brake pedal.  Still very little play, kills the engine with much pressure.  Rear drums, after shutting off, turn suitably.  Front disc are yet very tight.  A little less on the front left, and won't budge on the front right.  

(Point in question, while running the motor, and putting into gear [1st and 2nd] the left rotor turned, but the right rotor did not turn.  Is this normal?  Or is the right caliper malfunctioning?)  ( I expect this isn't likely, but is the R rotor causing both front discs to be tight)

My assistant, who pushed the pedal, while bleeding the brakes indicated that the pedal felt particulary resistant when the right disc was being bled.