UBS and it activity in buying/selling, page-3

There they go again, UBS lodged a "becoming a substantial shareholder" notice. To my totally inexperienced eye it does look like short selling because they note that stock is received and then returned. I'm surprised that all that activity generates enough profit to make it worthwhile. Any one have any idea why GXL is attractive for this sort of trading? It almost looks as if they generate the bulk of daily trading...makes me wonder if UBS are playing some of their clients off against another group of their clients? Surely they wouldn't do that just to generate fees?