I've posted the question
here on the B&M forums. Honestly, the only time the question came up (I'd played hours) was when I took a smoke break, came back and found out I couldn't buy the BB (in SB position) because of the rule. I didn't pay a lot of attention to how it worked before that point, so if someone could fill in the details on this concept (I'm not entirely sure of all the details, should have grabbed a rule sheet but just wondered instead) in that thread, maybe it'll make more sense to all players.