Stupid Siege Unit AI?

I'm making an AOS with subbases defended with towers.

But for some reason the siege units (mortar teams and Meat wagons) just walk past the towers into the base and shoots at them from the other side. o_O

When the siege units meet ordinary units they attack correctly, but not when they meet the towers. Any ideas? :\

EDIT: Actually they seem to be ignoring the towers entirely (and maybe all buildings), they only shoot inside the base if they can hit normal units.

Pft.

I had disabled attack two, which is the attack that targets buildings. Me feel stupid. :(