I just done Dust Palace twice in a row, the first one at the end when the last Flayer died I saw 2 blue engrams go over the edge, didn't think much of it cuz I figured they would be at the postmaster. Then the second time the last Flayer dropped 3 blues I picked up 2 (cuz my primary was full) & went to the Tower and postmaster only has 1 item & it's the primary I couldn't pick up from the second one.