What qd's are you using? Although qd's are "standard", there are still some minor variances between them. Are you sure you have the qd enplate facing the right way? If you look inside the qd hole in the endplate, the thinner (less deep) lip faces outward (the thicker portion faces inward). If you place it in backwards, there may not be enough space behind the endplate for the swivel to fully lock in (the qd swivel could bottom out behind the endplate before the qd's ball bearings seat into the cut out). Check and make sure the endplate face outward (thinner lip inside hole facing out). You would think the thicker portion faces out, for more strength, but it's the opposite due to clearance issues.