I am curious as to why?
I just encounted a flying protectron that crashed down from out of the sky and its ID started with FF.
*edit* or anyone else that may know.
No need in this anymore, but thank you

Source of the problem founded.
Why not FF? With MMM installed, all creatures can be from vanilla (with ID = index in FOMM) or from spawn (with FF in the beginning)
They always spawn together. FF creatures not possible to track, but from vanilla- easy.