You can't open any UI when you have teleported trough a nether portal

To reproduce:

1. travel trough a netherportal
2. stay standing in the nether portal
3. try to open any UI
4.  You can't

I know why you can't open a UI when travelling trough a nether portal, but I can't see any reason for not being able to open a UI when standing useless in a nether portal.