This is different from the other bugs that have to do with ender pearls thrown into portals: Here, the ender pearl actually collides with the portal (or the obsidian blocks around it), causing the portal loading screen to appear and the sound to play. The player is almost always not actually teleported to the nether, though.
This bug does not occur in survival mode, only in creative mode.

Steps to reproduce (video is attached):

1. Enter creative mode.
2. Build a nether portal.
3. Aim at the bottom face of one of the obsidian blocks at the nether portal's top (so slightly in front of the actual portal blocks).
4. Throw an ender pearl.
5. The loading screen appears and the sound plays, but the player does not get teleported to the nether (at least in many cases).

What I expected to happen was:
The player always gets teleported to the nether because they are inside of a portal.