On Thornbird i'm seeing this, I like to use multiple chat windows for things rather then tabs. What I am seeing is the chat windows just seem to go poof on their own, I will look away and look back and one or two of them are just .. gone. No camping, no zoning .. they just poof I can easily reopen them again but all filters I had on them have been reset. I've never had this problem on any other server I have played on.
Is it possible you have the "escape to close" option checked on your chat windows? And you are hitting escape.
