You can go through a portal while being dead

If you die inside a Nether portal before being teleported, or if you die while having some velocity and your body moves into any kind of portal (including End portals and gateways), then you will end up teleporting. This happens in both Creative and Survival gamemodes. After appearing on the other side, the "Respawn" and "Title Screen" buttons are grayed out for a second again.

I would expect that your dead body can't go through a portal, because it cannot interact with the world in any other way either.

Here are what I have found to be the easiest ways to reproduce the bug:

• Nether portal: In Survival, set up a command block that will kill you near the portal, and trigger it while you're in the portal. In Creative, grab an Elytra and fly towards the portal, but use just /kill before you get there (it helps to make the portal large).

• End portal: Fly high above it and then fall down. Type /kill just before you reach the portal.

• End gateway: Remove the obsidian and do the same as with the End portal. It helps to open the debug menu so you can verify that your coordinates changed.