Usage of Neither, Either in a Sentence

Well they're a bit confusing. I think that the question I'm seeing right now is grammatical, but it does not seem very clear or graceful.

Each is ambiguous, more because of your use of negations with “both” than because of “either” or “neither.” Your words “not present in both” might mean “present in only one” or “present in neither,” or it might regard those two as being practically the same. And similarly your words “not used in both” might mean “used in only one” or “used in neither,” or again, they might mean to make no such distinction.

Personally I also find it unclear. The hyphenated words are a jargon whose grammar and meaning I cannot guess.

Would something among these choices capture your meaning?

1. Any item which is absent from both menu-source and menu-editor is neither edited nor added.
2. Any item which is absent from either menu-source or menu-editor is neither edited nor added.
3. Why were key-up and key-down disused in both cases?
4. Why were key-up and key-down disused in either case?
5. Why was either key-up or key-down disused in both cases?
6. Why was either key-up or key-down disused in either case?

They're not correct, I'm afraid. Sentence 1 has too many negatives and sentence 2 needs a verb after 'Why'. They could be rewritten as:

Sentence 1

An/any item absent from both the menu-source and the menu-editor
has been [or can be or should be] neither edited nor added.  

or

If an item is absent from both the menu-source and the menu-editor 
it has been [or can be or should be] neither edited nor added. 

Sentence 2

Why aren't the up-key and down-key used in such/these cases?

or

Why is neither the up-key nor the down-key used in such/these cases?