Very confusing indeed. I love the concept of BitShares, but all of these rules/restrictions on trading activity are ridiculous. Just let the market work naturally for god's sake. It's what people want.
Whilst it would be great if things were just simple, what has been happening in reality is that when BTSX hits a peak, everyone desperately pays +20% for BitUSD. When BTSX hits a bottom, people pay less for it.
So instead of being pegged dollar, BitUSD just becomes some kind of trading game. That's what these rules are trying to solve.