When I read this:

Important: Lua functions are not supported.
Due to the savegame serialization of Factorio, Lua functions cannot be used in this mod

I understood "Lua functions" to mean all functions that are part of Lua (built-ins and library functions), like type() and table.insert(). But I used some in my code, and the combinator worked fine. So I moved on.

Then I got the error message when saving, so I came to the "Discussion" section here to see how I could use the combinator without using any Lua functions. After reading through it, I think you mean something like:

Important: Declaring custom functions is not supported.
Due to how savegame serialization works in Factorio, custom functions declared with the function keyword will cause game saves to fail.

Or something similar. Care to update the "Information" page to be more clear?