When opening the codex on a page that :
- includes a building info panel
- is longer than what the screen can display
- but wouldn't be longer than what the screen can display if the building info panel wasn't there
then the page initially doesn't have a scrollbar and can't be scrolled through (mouse wheel or drag). I'm assuming this is because the info panel has an appearing animation which means it's not considered at first. When switching to such a page when you are already on another codex page makes the scroll behavior work correctly however.
This happens for example with the mini-miner, pin pusher, painter, fluid tank, belt reader, button, display, and shape analyzer pages.