Actually, part of this is a bug - it isn't possible to make a layer stencil to itself, combustion should not allow this. Even turning off "Invisible to Camera" still won't make the layer reappear, this is just something you shouldn't do, stencil should always use another layer, that's the only way it can work.
Otherwise, the automatic switching of the Invisible to Camera button was put there so that the stencil layer doesn't appear on top or behind the destination layer while being used as a matte.