[Haskell-beginners] Help : foldl skipping one value in list

[Lev Broido]

Hi
I am implementing toy loop search algorithm in graph .
I encountered strange problem -- it seems , that fold doesn't run on the 
whole list .
Code is at http://hpaste.org/53776
Section in question is updVis function
Problem occurs when _newStateMap_2 is being calculated
Please advise.

Thanks,
Lev