Well, you have this event:
Enemy worm head is outside of layout
> set worm advise x - to enemy head x
> set worm advise y - to enemy head y
So they are at the same spot..
I always thought two things in the same spot have a distance of 0
So the text is completely right..
But you forgot the Advise have a "Bound to layout" so the advise not is spoted at the enemy because he can't move. to the X or Y .
If you set ever 0.1, etc... like chadorireborn says, the distance works correct.
EDIT: I guess is a conflict with "bound to layout" that not left the advise go to the enmy and the distance that seems that to work too fast appears 0. Sure if i get another event instead "bound to layout" that works equals the distance will be fixed. But i don't know how get the same thing in the advise to appeasrs only around the layout without the "bound to layout" behaviour.