Unit unexpectedly moves instead of attacking

[beorn]

1.0.0.38

The archer sitting in Athens encampment moves instead of firing at the Spanish cavalry corps.
Why? The encampment can fire at that unit from that location. And the archer shows an arrow rather than a movement path when I left click on the cavalry with the archer highlighted.

So instead of firing from the encampment, where he is relatively safe, he moves to the wonder to the northwest -- where he can fire, but where a counterattack will destroy him in one turn.

Bug? Design problem?

Saved game just prior: http://www.bemont.net/PERICLES 244 1665 AD.zip

 

[DemonMaster]

... or both a design and bug.

I have done this mistake multiple of times. I know that to be sure that the unit will do the right thing I must use the ranged attack button but I usually use left click and every now and then you move instead of firing for some reason.