All well broken in smooth operating pump guns SHOULD do this. Its just like an inertia gun with no spring to return the bolt to battery. You pull the trigger and the hammer drops, which unlocks the action, but the bolt does not unlock until the fore end moves to the rear. The recoil throws the whole gun back, fore end, bolt, and all, and you stop the receiver. I can shoot my Wingmaster one handed and it will do this every time. I cannot believe how this question keeps popping up on gun forums, and the uninformed always say run to the gunsmith.
It usually pops up every year when folks are sighting in their slug guns from a rest, not standing and shooting normally, too.