I won't say they can't move on their own. But if they are, keep an eye open. They might be preparing to take over completely.Maybe just as base got more inflated it appears to have moved to hanging over the edge like in these 2 pictures below and as it inflating then deflating it slowly moved a little tiny bit each time.
And as for always open ,is this saying to me they hungry and trying catch small particles in water or telling me they dont taste nice to fish or even toxic so at night time they dont need to close as no fish will eat them kind of thing ?
I know if hermits climb over them they close and half closed at moment which dont see that often really