Yes, you're right - I've just tested this too, and flg_p_open_opp is never true if you're in the SB.
I don't know whether this is intentional or not - there may be a definition issue where you can't 'open' if you already have money in or something, although that doesn't make sense to me in this case. We'll have to get a ruling from Josh or Derek.
You could create a ticket on the
Support system , and link to this thread so that this doesn't get lost. If you get an answer, please post it here too.
For now, you can filter for "posted SB" AND "chance to steal".