Strange characters (looks like key codes) show up at startup/shutdown
 

This does not seem to cause problem, but anyway it is strange.

When my system is booting / shutting down, occasionally "^@" appears at the beginning of some lines (as if I have hit some key when no input is expected by console program - but I actually have not). Especially this occurs when DHCP client shows it lines of requesting server and "done" line. Sometimes this stranger character occurs at shutdown, too. What could be the reason?

Debian 6.0.5, linux 3.2.0-0.bpo.3-amd64, Lenovo IdeaPad Z580A. (What else should I probably report about my system?)

Merely a remark: "^@" is a zero byte (or null if you prefer).

Just have noticed that this combination appears if I press "Fn" key during the boot. But it sometimes does appear without pressing anything.