This is something that just occurred to me, but I'm away from my books on vacation.
Can you interrupt your movement action to take another movement action, immediately resolve it, and then continue with the prior movement action?
This might sound like a big fat
"but why?"
, but I realized that when it comes to certain terrain features, this could be used to get the large monster across pits or elevation lines, interrupting movement in front of them, extending over them (without stepping into them) and then moving out of them/across them.
Rules-wise, avoiding things like this is usually handled by forcing the OL to declare their action before interrupting, and also have an available action to actually do (that is, if you can't attack, you can't interrupt with an attack, obviously).
I think it'd be fair - you're still spending an action. But it's also a way for monsters to completely avoid certain obstacles if they're expected to take two move actions anyway. So I'd fully expect the players to go
"You cheating bastard!"
.