Program disappears when minimized

[Aweck]

Hi: My system is Linux Mint 14 Nadia 32-bit. Whenever I have any program (such as Firefox or a file browser) open on the desktop and press the minimize sign (-) on the upper right-hand corner, it closes. To bring the program up again, I have to restart it, and the previous program settings are gone. How can I fix this problem? Thanks. Aweck