The "issue" has been an issue with the Maps app since iOS 4, I've reported it to Apple. There's something going on with the "Country" tag - I'm in the "United States", tapping on a Contact's address, for instance, and in not all cities (which I can't explain why it's just a localized problem" lands the Maps app's pin in one place - but then editing the address in the "Search or Location" data field to delete just the words "United States" and searching again drops the pin in a different place.
For instance, I'm wanting directions to somewhere here in Portland, and the pin gets dropped exactly where it should be with the full address in the Search field (which includes "United States". But tapping on the address for one of my attorneys in Vancouver WA United States drops the pin about 1/3 mile from his office - deleting the "United States" from the Search field drops the pin where it should be. Tapping on a friend's address in Vancouver is exactly where it should be, but my mom's address in rural WA is affected like the aforementioned attorney, about 1/2 mile up the road from where she lives until I delete the "United States" from her address. BUT...
It's not just the Maps app. Mapquest finds all addresses correctly no matter how they're entered. Telenav can't find my attorney's office exactly no matter how they're entered - but it does navigate to the same wrong address that the Maps app shows with "United States". Bing finds the attorney's address without the "United States" tag but is miles off with "United States" AND without it, but is nuts on if I delete the "United States" and the ZIP code. Go figure.
It's not just the Maps app...