Yep, I found that out too. Dropping out of the 'Transparent' state is something I've always hated about the Setiemson perfume... and now it's my chief complaint about the Vanish Mantle. The only way to avoid turning visible is to not 'act'. So, the V-mantle and Setiemson (which also Hastens your character for the full duration of the battle regardless of whether you 'act' or not ... ) are only useful for positioning a character in a strategic location without any enemies taking notice..until it's too late! Invisible characters can also be used to clog up a narrow passage or stairway limiting enemy movement.