When playing in single player, if you pause the game while looking at a nether portal, all other particle effects in game pause where they are, but the animation of the nether portal (the swirling effect) continues

What I expected to happen was...:
Since all other effects pause, I expected the animation to pause as well

What actually happened was...:
While all of the other effects pause, the swirling animation continues while paused

Steps to Reproduce:
1. Build a nether portal
2. Pause the game while the nether portal is in your field of view