Bytemaster, can you please explain why this was implemented like this?
Because collateral is not "moveable" and would require a new type of buy order... "buy with collateral, and relative buy with collateral" these orders would be added to our existing 3x3 matrix of potential order matching which would make a 5x3 grid of potential parings. Not to mention the fact that while orders are in this state I would still have to consider them for margin calls.
So for the sake of simplicity I decided to separate concerns *AND* because it creates an implicit requirement for extra collateral.
One thing I could do is trigger an "immediate" margin call by raising the call price to the current feed price. This would immediately cover your full order and I could even have it bypass the 5% fee in this case.
"immediate" margin call needs to be added to bitshares in order to make this realistic to trade. I have been trading for over 10 years and I can gaurantee you we won't see adoption with the way the rules are currently laid out for covering shorts. We are literally being trapped in positions until the 30 day holding period expires or our collateral drops below 1.5x or 2x... I don't remember which one it is.
What if I have 100,000 bts and wan't to take a short position at 100bts/usd and risk up to 110bts/usd? In real life trading a trader will position his trade size so that a loss = 1% to 5% of his account, so I would risk say 2,500 bts (2.5%). That would mean my position size would be short 250 bitUSD. Collateral would be 75,000 bts for this position. I would still have 25,000 bts left over in my account. Lets say the price moves in my favor... Great, my bts is worth more and I can buy 250 bitUSD on the open market and cover my short and have a few bts left over. But now lets say the price moves against me and I wan't to cover my position at 110bts/usd... BUMMER! my bts is only worth 227.27 bitUSD and I can't buy enough to cover the short. I'm screwed until I get a margin call and my losses have most likely exploded past my stop out point.
This destroys all possibility of practical risk management. The risk is asymmetric to the downside. I can't stress enough how badly this needs to be fixed. Just look at the nightmare that the swiss franc caused a few weeks ago. It bankrupted many people and many exchanges all because they were unable to get out of their positions.