Immediately after I activated the ability on my Ottoman Bombman, my opponent played Papal Bull on the Bombman. By the time I had selected a Site to bring back to my hand, the Bull had resolved. At that point, clicking "Confirm" on a selected Site had no effect. None of the Sites in the Archive could be selected, and I was stuck in the card selection screen until the game ended.
(Given the timing, I suspect my opponent was aware of the bug and was deliberately taking advantage of it. Is there a venue for reporting potential bug abuses?)