There my Dutch army sat, confidently awaiting the approach of the Spanish army across the valley.
And as the enemy infantry marched near to the maximum range of cannister, I toggled the cannon from roundshot to cannister. The enemy infantry immediately about faced! I had to check what I think I saw. Did the AI just react not to what my troops were doing, but on a mouse click I made?
I opted to check, so I toggled roundshot again. Instantaneously the Spanish infantry about faced once again and marched towards my lines again. Switched back to cannister, retreat. Roundshot, advance. Repeat ad infinitum.
To make it absolutely clear: The enemy AI wasn't reaction to cannon fire, but merely to the type of shot selected. Not a single shot was fired at them to make them change their mind about the attack. I finally just selected roundshot and Hold Fire to coax the AI in to my field of fire. Only then did I switch to cannister and ordered them to open fire.

While I don't mind that the AI gets a look behind the scenes to check what I'm doing in order for it to cope better, I do hope it gets hidden a lot better then this! It's just creepy and wrong to see the enemy take it's cues from me so directly.