Modifying a TSDZ2 for rear braking

I ordered 3 x TSDZ2 36V mid-drive units from China.

They should have all been identical and functional with a hub gear and brake on the back wheel (Nexus 7-gear) but unfortunately two of the units are different.

The first I installed without a problem but the other two have the crank free-wheeling when I attempt to apply the rear brake.

I presume this meant for downhill, de-railer gear system not hub gears with a hub brake?

Can anyone tell me what parts I need to order so as to make the modification required?