It slips when tightening up. When the jaws touch and I keep tightening it the QR handle starts moving towards the screw – the half nut moving downwards away from the screw. This happens only if the jaws are open less then about 4″. It feels like the screw is not “biting” into the nut and instead doing exactly opposite.
So as a result, I can clamp pieces wider than 4″ without an issue. For everything smaller I need to hold the QR with one hand and tighten the vice with other hand. A wedge might be used however I do not want to loose the QR function.