This particular bug was a display issue... it was pulling in all USD shorts from the USD / BTSX market as if they belonged to this market.
BTSX will not be supporting asset/asset shorts for a while.
BTW, I do not know how much pulling is involved (from the bitUSD market), sounds more like pushing, because
I managed to place the displayed order using the GUI as a short bitUSD, using bitBTC as collateral (had some bitBTC).
Just so you know.