This question hasn't been answered yet, so I decided to write a specific post on it.
This multiplier is mostly applied to most status attacks, but is also applied to a number of other spells.
The behavior of this bit is to induce a 1x multiplier for both the spell multiplier and magic defense multiplier (0 is used for monsters under most instances, 1 is used for characters that have at least a magic defense multiplier of 1) in the spell algo.
I wondered whether to keep calling it the status multiplier.. but it may be more appropriate to call it the solo multiplier. I do need an answer to this...