I just ran into this as well, I posted something over in this other bug that seemed to apply:
https://github.com/ValveSoftware/steam-for-linux/issues/2608
That's it, I couldn't find that issue with any of the search terms I used.
Closing as a duplicate, then :)
When attempting to purchase products from the steam store I found I would be blocked with a message to verify my country. After checking on my Windows PC I found that the boxes marked "I currently live in the country selected above" and "Save my payment information so checkout is easy next time" were checked by default, while on Linux they were set to the "-" symbol. Clicking them would set them to "checked" but the store would interpret them as not; however, setting them to "-" would have them interpreted as "checked".
Ubuntu 13.04 64 bit