Nether portals lit becomes unlit after relogging into the world.

Steps to reproduce:

1. Build the portal frame where either or both of the two obsidian "floors" are in a chunk border (e.g. 0,?,0 and -1,?,0 or 0,?,-1 etc.)

2. Light the portal using flint and steel/fire charge/fire spread.

3. Save and quit the game.

4. Enter the world again.

Expected result:

Portal should be still lit up.

Observed result:

Portal is gone/deactivated.