If you login from a new location it seems it flags your account - Probably for security reasons, they're trying to avoid lots of "Someone hacked my account!" support issues. Steam does this as well and probably other services too, but there's no way to "opt out" here.

The only (at least unofficial) solution seems to be to use a security token on your account (hardware or software) and then the IP checking is ignored, presumably because the one time password adds quite a lot of security so they don't feel the IP check is necessary.