Warning: don't deal with 796.com!

2 weeks ago I've bought LTC at ~$5.00, have sold and opened short position at ~$6.00, and closed short position at ~$4.5 (on July 11)
my net profit was ~550 LTC.

I have seen this profit on my account balance but it has disappeared soon.
when I've contacted support, they told me they have "socialized" 73.97% of profit of their users because LTC price moved violent last week.

https://796.com/ltcFutures/settle?lang=en here you can see that 796 guys have "socialized" or maybe "expropriated" 73.97% of profit of
their users on July 11 and ~45.1% on July 4.

Is it legal? Have you ever experienced something like that with btc-e or other exchange margin trading?
Is there any scam list to add this service ?