When a shulker enters a nether portal, it's coordinates do not get divided or multiplied by 8. If you create a portal at 1000, 1000 in the Overworld, and take a shulker through it, it will spawn at 1000, 1000 in the Nether (and vice versa)
This works similarly with end portals, if you push a shulker through an exit end portal, it will appear at coordinates 0, 0 in the Overworld, even if world's spawn point is somewhere else.

(I'm hoping this will get fixed soon because the shulker is needed for the "How did we get here?" advancement)