compound nouns and noun heads

[zaba]

I'm looking at compounds and see a funny (but not hilarious) division.

1. boy-baby = 'infant son'
2. kiss-sickness = 'oral herpes'
3. excess.fat-people = 'the obese'

In all these cases, the second noun seems to be the head, agreed?

But what about this:
4. cake-gnome 'a traditional cake shaped like a gnome' (eaten during a specific ritual)

Here, the first noun seems to be the head.

How does one account for this difference?

[Daniel]

More data! There's no strict requirement that there can only be one order, but that is strange.

Is there a possibility this is a borrowing?

[zaba]

It's the only one that I found that has this sort of formation. There's no reason to believe that it's a borrowing. How can I describe this difference in compound formation??

[Daniel]

A footnote

Without more data, there's nothing to say at all, except that this is different. Worth a note certainly.