I'm using the trakt plugin, and I just noticed that it is reporting the wrong time to the server when marking a show as watched. I just marked a couple of episodes and instead of 23:30 which was the time, trakt shows that I watched them at 01:30 the next day.
My guess is this is a timezone issue. I live in UTC+2, and the trakt setting is set to that hour. The plug-in is probably using the local time while trakt expects a UTC time, and then trakt adds another 2 hours to match the timezone.