Zones and "national of computer" problem

[Rzebina]

Hi, I have strange problem. My shipping is working perfectly except for one case. Presta looks like she (he? xD) select zone by national of computer not country/state selected by user. Example:
User is making order from England but he have computer bought in Germany. Presta is showing him prices for shipping to Germany, not to England.
How can I deal with it? Thanks for help.
I use Presta Version 1.3.2.3

PS: I'm sure zones, countries etc. is configured correctly.

PS2: One more thing. It doesn't work like this every time. When I set my country to for example Germany shop is giving me correct prices even I have polish computer. I think it only involves new customers whos typed their country on registration.