I have observer a very large hole in Gmail. when going to certain sites with Gmail open in another tab. Gmail signs out well your at the other site. I have noticed this a few times now. I believe it to be some kind of cross site hack that if you sign back in well at these other sight they can read your log on credentials. Or are attempting to from the other sight. If you do suspect a site of doing this.
QUIT THAT SITE before signing into Gmail again!!!!!!!!