Check the operation of the secondary master cylinder which is located above the LH front calliper. Centre pot of each calliper is operated directly by the foot pedal.Hand lever operates the front calliper outer pots directly.Any braking on the front wheel (by foot or hand) causes the LH calliper to operate the secondary master cylinder which then applies the outer two callipers on the rear wheel.
the foot brake is operating all three pistons on the rear.
Possibly rear master as well.......may not be allowing fluid to return. I leave callipers mounted and just remove and replace the pads (they slide out/in) when I do mine.
Possibly rear master as well.......may not be allowing fluid to return.