All units with MTW2_Spear in battle_models file's animation section do not use their weapons to attack in battles, but stand idly.
I can change it to MTW2_Fast_Spear (it fixes the problem) easily enough, but it changes the animation too and does not look good for longer spears. What could possibly cause such a bug? And is there a way to fix it?
Only for a specific mod, by the way.
Another interesting thing is sometimes the bug occurs even after I change the attribute. For those units the only way to fix it I found to be changing their "soldier" entry in the EDU. Now, I read that changing it, changes the unit's appearance, but it doesn't. For me at least.. I replaced the entry for the buggy spear units with "order_spearmen" (a spear unit which works without problems) and the bug is gone.
After that I try changing their weapon animation back to MTW2_Spear but it seems it doesn't work anyway.