The nub it locks into on the cap side is the bypass valve. While it can move somewhat under friction, it is suppose to remain static with the housing side tip o-ring is suppose to spin as it is screwed down with the outside media of the cage somewhat floating and not rotating a as much if at all as the cap is screwed down.
I first noticed this on standard WIX cartridge filters and now this Hengst. Not saying to not use them but they would not be my preferred Pentastar cartridge filter. Point is moot for me though as I went to a Baxter Performance filter adapter and use regular can filter.