Running version 1.12 pre7 . Had the same issue on 1.11.2
Running on a private server running the same version.
When trying to pass through the portal a wall of dirt is presented.
After rebooting and logging into the game again my character is at the same co-ordinates in the nether as it was in the overworld.
I am reporting the problem because it is flagged as resolved in previous versions.

Thanks for your help in advance.