The AI constantly flees from the battlefield.

It's also annoying, but from the AI's perspective, the logic is this: don't give us experience, considering that it won't do significant damage anyway. Sometimes it runs away due to bugs, especially if "dodge" is used – a completely broken spell for the AI. There are two solutions:
1) Find shackles (obvious).
2) Bring out a single stack and defeat the army using tactics.