I have not seen the AI break a siege in 1.5/1.6 but I believe this can happen if a threat occurs elsewhere, particularly its capital.

Save/Load definately alters diplomacy. After reloading the AI is more likely to refuse offers which it would have accepted without the reload.

AI armies within enemy territory still seem to withdraw back to within their territory after reloading. The exception seems to be when the AI is absolutely determined to beseige you.

The AI seems to not want to repair or retrain after reloading. I'm not sure if building and recruiting is affected.