I have a strange error.

I sold on margin some 10 LTC on LTCBTC pair.
Then I sold 10 more.

But I am holding a long position on 20 on LTCBTC pair.

WTF?!?!

Did the buttons malfunction or something?
Is this error related to the one where you click sell, while "Market" is selected and your order gets placed as LIMIT instead?

Actually, I checked the history and it says "LTCBTC    -10.0    0.007852"
Is that a sell order? then why am I holding a long position?

I checked the last 12 days of offer history and yep... only negative numbers in LTCBTC, yet, I hold a positive position.

You little rascals!

The math says that you must have had 40 LTC to start with.  But I wouldn't doubt that the problem is with the display and that you started at zero and now have a short position.  They recently fixed a problem I mentioned with "available balance", so there might be some residual display errors.  Hopefully they aren't math errors!

If you use maximum leverage, your initial margin is 30% - out of your total position size, you pay for 30% yourself and take out swap to pay for the other 70%. The amount you owe to the swap provider remains fixed, so as the price goes against you and the total value of your position shrinks, the percentage of it that's marked as "owed" increases, and the amount that you own "yourself" shrinks. If that part shrank to 0% you'd have a position worth exactly what you owe and would absolutely have to be liquidated immediately to avoid loss. For safety, the margin call comes when 'your' portion is 15%

So if you started out with the price at $200, with $100/0.5BTC of your own, you'd be able to borrow and sell another 1.166BTC to get $233, bringing you up to a total of $333 of which you provided $100 (30%). You'll continue to owe your swap provider 1.166BTC, so your position remains open until the position as a whole is worth 1.372BTC - at that point you have 1.166 owed and 1.372-1.166 = ~0.2BTC owned, (and 0.2 is 15% of 1.372, or at least it is when you use the exact numbers rather than these rounded versions)

Since you have $333, the specific price point where that's worth 1.372BTC is $242/BTC, but the maximum distance from your starting price will vary - it'll be the same percentage difference each time, so long as you always use the same degree of leverage, and it'll be more "forgiving" (further away) if you use less leverage, since you then start out owning a larger percentage of your position, so it takes longer to shrink down to 15%

tl;dr: Your margin call comes when (Position value - Swap debt)/Position value ≤ 15%

Or to rearrange that a bit, when Position value = Swap debt/0.85 (since your swap debt is a fixed quantity you can calculate that one ahead of time and work out what pricepoint implies that position value)

I thought they changed that a while ago, so that if you go short against a deposit of BTC or long against a deposit of USD you "borrow" (without any fees) from your own funds before you take any swap. I remember an announcement saying that they'd realised that the way it was set up you effectively got more leverage by holding your deposit in the same currency as you were borrowing, and that the change had evened it out so that it didn't matter which one you started out holding.

if you could provide the relevant order history, we can figure out why you have a positive balance when you said you have sold the pair. I don't think there are these type of errors in the platform as you have claimed

Is this and other swap behavior subtlety documented somewhere?