Format Bug When Date is > '1/1/2007'?

Has anyone encountered the Format( aString ) function behaving
differently asof 1/1/2007? I'm seeing this:

Format('070102-1') results in '1/01/4566'

and

Format('061227-1') results in '061227-1'

(as you can tell I don't usually delve into VB). This is stuffing up
one of the feeds we've got that have been working since 2003.

Anyone got any information on this? (The solution is easy, remove the
Format() function, but I'm curious as to what the cause is).

.