Wouldn’t an experienced mechanic realize that the brake bleeding valves were at the bottom of the caliper and pointing down instead of like they should be, at the top of the caliper and pointing up? On first inspection?
I can see how a DIY’er might reverse the calipers side to side. But an experienced mechanic who’s addressing a customer complaint about air in the system and is charged with bleeding the brakes not noticing the bleeding valve is at the bottom of the caliper? Or would this problem be more difficult to observe than it seems?
That’s my thought as well, George. When the pro at the shop found out he’d rebuilt the calipers they should have checked his work first even if they didn’t immediately realize what he’d done. Just to replace multiple master cylinders without even considering he may have done something wrong seems pretty amateurish.
Maybe he didn’t tell 'em. 
Regarding my comment, I realize how appropriate my choice of user name. They should have immediately known what was wrong when they bled the brakes themselves whether he told them or not.
Visual inspection is the first step in any diagnosis. Foolishness.