whenever i partially destroy a portal in the nether (the 4 floor obsidian blocks are left), then die and reenter the overworld portal, there's a chance the nether portal won't respawn, and i'll end up standing on those 4 obsidian blocks with no portal behind/around me instead.

destroying those blocks will respawn the portal next time, but as long as they're there the portal has around 50% chance of getting respawned.

it's like minecraft still treats those few remaining blocks as a working, active portal.

edit: this actually happens as long as there's even one obsidian block remaining, even the top ones.