Google maps mobile goes 'home' when lost?

joseph barrows writes: "This morning I was at my girlfriends place (some here may need to google that phrase) and checked googlemaps on my mobile to find my way to work. I do /not/ have a GPS so rely on the tower system for 'my location'. Google and/or my telco reported my as being 30k's away, at my home address on the other side of the CBD (with better accuracy than I get when I am at home). Any one seen this behaviour before? or know how and why it did this? I'm pretty sure I wasn't 'roaming' as I was still within the Melbourne metroplis.
Surely if the system doesn't know my location it should admit that rather than give misleading information."