I had this kinda annoying bug on my channel since the very first day. When you browse the game directory from the game I'm currently streaming, my channel preview will be shown as a default image such as:
I reported it through the help support on Twitch site but the only answer I got so far was "Are you streaming use FME?" I answered such a mail and haven't got any more feedback. The answer is no, I'm using Xsplit Broadcaster.