When riding a minecart through a nether portal, the direction you are facing is set to pointing directly south, with no pitch. Looking at F3 shows that this is (0,0) (0 yaw, 0 pitch). You would expect that the direction you were facing when you entered the portal would be the same as when you exit the portal. This works as expected if you walk through the portal, but not if you ride a minecart through. This does not happen with horses, boats, or saddled pigs, just minecarts.

Steps to reproduce:

1. Press F3 to bring up the debug
2. Ride a minecart through a nether portal while facing any direction
3. See that once you exit, you will be facing south and looking at exactly 0 yaw, 0 pitch.

Here's a video
https://imgur.com/fTWOUje