Depending on the machine i log into (cookie’s?) i see old chats pop-up, which i closed before.
Expected behavior is once i close a chat on one machine, it will never pop-up on all other machines, independent on cookies.
We have several bugs turned in on the bug tracking system for this issue. Here is an example: http://goo.gl/mKHTWR.
Just to let you know we are aware of the issue. 
I assume this is about personal messages, not chat, right?
I believe it is for PMs.