No idea, but it happened to me too. It appears to be a mistake they made when closing the HGHTEST stock.

no. when a stock goes long from under $50, and you're holding it short, you lose more than you put in.
For example, if I'm holding 1000 shares of X stock short at $20, I lose $1000 every time the stock goes up a buck. If the stock goes to $100, I have just lost my investment ($20,000) plus another $60,000.
It's happened before and isn't an issue or bug.

You lose more because when you short, the market is saying that it guarantees that it will buy the shorted stock from you for the shorted amount. Here it is a little different than in the real market but it is close. Here the market holds the shorted value for the stock but does not actually buy anything except the promise of the market to buy the shorted stock from you. When the stock goes down and you cover you make money because you are able to buy the stock at the lower cost and sell it to the market for the shorted price. Conversely when the stock goes up you lose money because in order to cover (or pay out) you have to pay a higher price than the shorted amount. So say you shorted at $27 and it paid out at $100 (the system does all the work for you) it buys how ever many shares you have at $100 then sells them to the market for the shorted amount ($27) leaving you with a deficit of $63 a share, which if you have less than that in cash leaves you with a negative cash balance.

I started thinking and I believe the easiest way to think of shorts is as follows. When you buy a short say at $49.00 a share, (and keeping it the whole time and not short cover shorting) the most you can make if the prop fails and pays out at zero is your investment, and that same amount again in profit. so the payout would be your original investment (which is already apart of your net worth), and $49 a share profit (which if the stock declined over time some or most of which is reflected in your net worth). But if your $49 dollar short pays long, think of it as taking your initial $49 investment and having to pay an additional $51.00 a share to purchase the now $100 Stock, and then immediately selling that $100 share for your investment amount. So in reality the most you really lose is the difference between your invested amount per share and $100, because you will always get your invested amount back. Thats why shorting a stock at $98-$100 can make sense sometimes sure you tie up a large chunk of money by shorting at $98 a share but you only stand to lose $2.00 a share plus commission if the stock goes long, but if it fails you stand to make a $98 per share profit.

The easiest way to think of a short is by understanding what it actually is. You DO NOT "buy a short". Short is a verb. It means to sell. More specifically it means to sell something you don't own. How do you sell something you don't own? By promising to buy it back later no matter what the price is. If you buy a stock or short a stock profit calculation is the same. Sell price minus buy price. The difference is when you short you get the sell price first. So if you short a stock at $20, and it pays out at $100 (you buy it back at 100), $20 - $100 = - $80. You lose $80. If it doesn't pay out (you buy it back at 0), $20 - $0 = $20. Another important difference to keep in mind is that when you BUY you can only LOSE as much as you put in, while when you SHORT you can only GAIN as much as you put in.