Unbreakable Nether Portal in Vanilla

I created a nether portal, sized normally as a 2 x 3 portal, and when I tried to break the purple part it wouldn't break. I tried using my pickaxe and sword but to no avail. I tried resizing it and that didn't work either. The only way to break it is with the break-anything punch in creative mode or by removing an obsidian block from the side. I am not using mods or plugins. I am not sure if this works in multiplayer.

What I expected to happen was...:
Hit nether portal with sword/ pickaxe/ block/ fist/ powered piston

What actually happened was...:
Nothing

Steps to Reproduce:
1. Build nether portal
2. Hit
3. Be disappointed and annoyed at the nonstop whooshing noises from your basement while you're building something above.