Window-borders disappears in Unity

Solution 1:

Usually restarting unity helps. You can do this by Alt+F2 and then typing:

unity --replace

Note: Don't execute this command in a terminal otherwise unity will be killed, when the terminal is closed.

This is of course not a fix. Just a way to undo the error once it has occurred. I suppose these bugs (and the ones posted in my comments to your question) will be fixed with future updates. There are many bug-reports on launchpad concerning these.

You could also try ans install CompizConfig Settings Manager / sudo apt-get install compizconfig-settings-manager and play with the setting there. It might or might not help - depending on who you ask.