Bug in timed mode?
I have seen this multiple times today in timed mode. I will finish a translation and hit enter only to get a carriage return in the text box...and then a second later it times out without having checked what I wrote. :-(
It's hard to type quick enough to get some of the longer translation in before the gun, but to have it snatched with a bug is super annoying.
Hmm, I think this happened to me once but it didn't happen in my timed practice today. Staff do read these forums but you might get a quicker response if you also report it through the support tab.
Also, for bug reports it's usually a good idea to state your operating system and browser (including exact version numbers for both of them). When only some people are seeing a bug, this can help to nail down the culprit. (My non-buggy practice today was on Ubuntu 12.04 and Chrome 27.0.1453.110.)