Both Master of Many Style and Free Style Fighter allow the character to use several stances in the same time. If a character has, for example, 3 levels as Free Style Fighter and 1 as Master of Many Style, how would these features work ?
The wording of the Free Style Fighter doesn't seem to mention something about it :
At 3rd level, a freestyle fighter can freely mix two of the styles he knows into a more flexible style. A free-style fighter can have an additional style feat stance active simultaneously with his first style feat stance. He can enter all of his allowed stances as a move action or one stance as a swift action.
The description of the Master of Many Style seems to have more restrictions (emphasis mine):
At 1st level, a master of many styles can fuse two of the styles he knows into a more perfect style. The master of many styles can have two style feat stances active at once. Starting a stance provided by a style feat is still a swift action, but when the master of many styles switches to another style feat, he can choose one style whose stance is already active to persist. He may only have two style feat stances active at a time.
In this context, I don't know if the bold statement is only a difference of wording to track the Master of Many Style progression, so should be considered separately from the other archetype, or if this limit should prevent the multiclassing with the Free Style Fighter archetype.