Completely normal. It'd be unusual if your bolt didn't
go forward if the stock is bumped from the long axis.
Bolt's held in place by the catch.
BCG's weight, upon impact at the butt, pushes on the buffer spring enough for it to move slightly rearward, and the catch drops due to the tension of its own spring.
As the BCG returns forward due to the push of the buffer spring, the catch is no longer in its former place to keep the BCG from going fully forward.
Impossible to count how many times at boot camp somebody went from Port Arms to Order Arms with an open bold (not supposed to!), and have the weapon rebound off the deck with a loud CLACK! as the bolt drives home. Usually with the following result:
(Also completely normal)