I do not know if this has anything to do with the problem - I recently returned from a China trip and all my call history got changed so the phone numbers are now displayed with "+1" in front of them. More importantly, when my existing contacts call me the Caller ID does not display their name anymore, but only a number with "+1" and in a small font below "Maybe: [Contact Name]".
Of course, I can select "Add to Existing Contact", but do I have to update all my contacts now? The form with +1 is inconvenient to me and I would like to change it back. Is there a simple fix?