Replace Nulls not working when no value inherited

I am working on a patch which has an area in it where cables in the interface can be connected to achieve different things. Much like a synthesizer with patch-cables.

That causes some nodes to turn orange because they no longer have any input, which is expected.

Now I am trying to use the Replace Nulls node to substitute with a default. But in some sort of recursive irony Replace Nulls itself turns orange, when connected to such a node (see screenshot). 

Null item on the other hand does NOT turn orange when connected and correctly identiefies the input as being Null and Invalid.

Therefore I could build my own substitutor very simply with a few nodes, but really think that "Replace Nulls" should handle the same inputs as "Null item".

Is this a bug? If not I dont see the logic behind that.

Thanks, Armin.