Interesting that your 2012 ACE has an HWH jack system.....curious if this was original equipment or an add on replacement?
I don't have knowledge of HWH systems, but since no one has replied so far maybe we can start the ball rolling with some guessing. I think your assumption that the jack fluid return line or function may have an issue would be my first thought also. If it was a return valve physical open/close issue, I assume controlled by the rear jacks console lever set in the retract/store position, I would think that forcing the rear jacks with a separate jack would not work at all if the return valve(s) were closed (not allowing retraction.....since fluid has to go somewhere now being pushed by a secondary jack). So the first easy thing to do would be to trace the retract hydraulic hose(s) from the rear jacks and make sure it/they are not pinched somewhere back to the fluid reservoir. If that is not the issue then I would check out the console lever for the rear jacks and determine how it is supposed to open return valves to allow the return of hydraulic fluid. I assume the hydraulic motor is running when you try to raise the rear jacks? I also assume you have the manual for your unit (link attached). Failing that, a call to HWH might be the best solution......could be some simple component in the console unit needing replacement.