Note:

Survival mode players cannot see the selection box of the portal block (as intended). This means that when looking at a nether portal in survival, the player can place and break blocks that are on the other side of the portal, including the obsidian that the portal is made out of.

The bug

When trying to use a water or lava bucket in a nether portal on obsidian, nothing happens. In creative mode however, the selection box for the nether portal appears (as intended), but creative players cannot use water or lava buckets when looking at the portal whatsoever. Nevertheless, players in both gamemodes can experience this issue.

Steps to Reproduce

1. Create a Nether portal
2. Obtain a water or lava bucket
3. Attempt use it on the obsidian in the portal

Observed Results: Nothing happens. Neither water nor lava are even placed adjacent to the portal, even in creative mode.

Expected Results: The bucket is used to place water or lava and destroy the portal.

Note 2: The player can still use buckets in dispensers to destroy portals; it's only impossible if done manually.