Monster movement problem

Hi,

I have problem with my TFS engine.

The problem is that some monsters which are immune to some elements ( fire, poiso etc. ) are avoiding them.

For example dragon won`t step into fire field if he have clear path, without fire fields, to player.
If he won`t have clear path then he will step into fire field so that''s ok.

Anyone had similar problem? Or in which file should I look to find monster movement?

movement.cpp?
event.cpp?
creature.cpp?