You cannot build a nether portal in the end

When you try to build a nether portal in the end, the portal does not light up.

Steps to Reproduce:

1. Go to the end.
2. Build the obsidian frame of an ordinary nether portal.
3. Use the flint and steel on the obsidian.

Observed Results:

The portal frame has fire inside.
Expected Results:
The portal lights up and you can go to the nether.