Please explain "never mark for delete"

[edd]

I have a filter with "override delete" set to "never mark for delete".
I have "origin of spam" set to "auto delete".
I received a message that both matched my filter and was from a source of spam.
My expectation is this message would stay in the inbox.
But instead the message was put into the recycle bin
Is this a bug? If not, can someone please explain the meaning of "never mark for delete"?

[rusticdog]

Yeah I would consider that a bug, will add to the list to be fixed.

It might have been intended to work that way, but not intuitive if it was.