It's functional.
If you look in the socket in the middle of the windshield header where the "hook" latches. There is a micro switch that senses when the top is latched. If the piece is missing on the hook it won't activate the window safety switch. If the little piece in the socket is missing same thing.
The rear windows will not go up until that switch is pressed by the plastic piece that covers the hook in the top. Often the hook will keep cycling if the piece is broken.
You can reach in (popsicle stick?) press and hold it to enable the rear window switches to work.
Cab Top Latching Issue- Need help: Fuse issue or motor? - Rennlist Discussion Forums
Google the part number
996.561.787.00
If it isn't that part, one of the results should show an exploded view of the whole area.
Pelican info
Part Superseded to 9965617870101C (Click number for more info)
OEM-9965617870101C Genuine Porsche Part: CAP, ROOF CATCH.
- This is a special-order, non-returnable, Porsche part
(availability and shipping charges may vary). [More Info]
$9.00