lschnarch:
The AI is acting on code. To talk of it as being "stupid" is pointless. It has no true intelligence in the manner that we know it. All Civ AIs are like this. Several Civ IV AIs will declare war on you at times, even from Pleased status. The difference is that the numbers are transparent in Civ IV and you didn't have to figure anything out. It's not as transparent in Civ V.
All Civ responses are pre-canned responses that the AI issues in response to actions or whatever. True in all the versions of Civ. IF the Civ is complaining about your borders, then it is responding to code that's telling it that you're expanding too much or whatnot, regardless of whether or not your borders are actually touching. If it's complaining about units being near its borders, then something it considers its borders is being triggered by something that it considers your units.
Seriously, guys. It's an AI following a code. Always has been. Just because you can't see the modifiers now doesn't make that any less true.