Associated with bug 0010872:

I experienced this in my second siege attack.

I went through my first siege with it performing as expected. (an incomplete "dodge me" trap with too few Z-level a drop)

It just triggered my second siege attack and the goblins just walked right through my weapon traps set in my "dodge me" trap setup. as far as I can see there are no attempted attacks from the weapon traps as though they just are not triggering against the invaders.

There is no dodging being done from the Goblins to knock them down the pit, and I don't see any form of report stating any attacks (though I don't know if it does that normally)

About 80% of the attackers also walk right through my cage trap as well.