Save movement costs doesn't always work

[Plain Ian]

In Bulge Herbstnebel there are a few HQ's (US) which do not save movement points. The only thing that I can see different about them is that they do not have any AA values set? 

The supply units in this scenario do not save movement points either but I think that is standard. They do not have AA values.

Which rings a bell because I remember playing a scenario made by someone which had Supply Units which did save movement points and in his notes he said that in order to do so he had to assign an unusal value to the unit?

However as with many things these days....I may be havering............