There is an old note 131471 - Post difference: M7226 Update control of movement type
which added the M special stock to the MM inventory movements, in that note is a reference note 948337 which is about WM movement types. Unfortunately this note is not released, so you have to contact SAP to know what is in there.
At least I can confirm that I have no 711 - 718 movement type with M special stock in table T156S in my system and would expect to get the same error (we are not using empties management )