What I expected to happen was...:
I expected to be transported from the overworld to the nether (or vice versa) and then remain there, even if I did not leave the portal.

What actually happened was...:
I was transported between the overworld and nether until leaving the nether portal. In creative mode, you transport too fast to move out of the portal normally. Players suffering server lag or in creative mode find themselves trapped, sometimes for several cycles.

Steps to Reproduce:
1. Enter any nether portal.
2. Do not attempt to move outside of the portal, even after arriving at your destination dimension.