The only time I've seen this issue is when your previous order was to attack something that is now dead, like if you were moving to kill the bear cub that just suicided against your army. It's an extremely annoying bug.
I just saw it under different circumstances. Karavox took a city, then came out to fight two armies of pioneers standing on top of an outpost right next to the newly conquered city. He came out, but could not move despite having 3/5 moves left.
I saved, retired, restored, and he attacked without me telling him DESPITE me having canceled the attack orders before I saved.
----
It gets better. He attacked, won, and ended up on the tile with an enemy outpost and an enemy army.