What kind of negative growth do you mean? The float actually increased by about 70 thousand due to the short wall bumping into the buy orders.
If you are referring to the 0.82 USD/BitUSD on coinmarketcap I think that is because they calculate that price using various other ratios like BTS/USD, BTS/BitUSD, BTS/BTC and BTS/CNY. If some of those trades are a few hours it will mess things up.
If anything then BitUSD was actually trading above parity because the internal short wall ran dry.