It seems when you X out of the messages app and re-open, all of the previous texts are closed. I think this is a security thing so people cant see your texts on your computer.
it only shows up again when you have it X'ed out (but still open) and someone sends you a new text. You get a small text box on the top right. when you reply to it, it will open up the messages app and then show the rest of the convo.
I dont think this is a glitch.
That doesn't make any sense - if it were a privacy thing then why wouldn't Mail etc. work in the same fashion. I'm pretty sure this is a bug on my machine. I tried uninstalling and reinstalling it (rebooting each time) but the messages still go away