Hello, if you sneak on a hopper and then close a trapdoor, it stays that way in first person perspective. In all other perspectives you stand normally. You can also let go of the button.
The same happens the other way around, i.e. you stand on the hopper and close a trapdoor, in the Ego Perspective you stand, so the shift is deactivated. From the outside you are also standing, despite the shift.

You can see the setup in the attachment.