When you run the following AppleScript for an account that exists but a contact that does not and you have no open chat windows, Adium creates a chat window that is invisible and has an id of -1:
tell application "Adium" to tell account "accountname" to make new chat with contacts {contact "invalidcontactname"} with new chat window
You can see the id of the chat window with:
tell application "Adium" to get id of every chat window
After you have created one of these hidden windows, try opening a chat manually by double-clicking on a contact in the contact list. You get a chat window with two chat tabs, one chat tab has no name and is partially drawn. You can't close the chats by clicking on the icon in the tab, or by using the "Close Chat" option (command-w). If you try to send a message to the contact in the second chat tab it opens multiple chat windows in the window. If you close the window and try and open a new chat with the same contact by double-clicking on the contact in the contact list, Adium opens the old window (this might be normal if the windows stick around in case you open them again). The only way to get out of this weirdness is to restart Adium.
