Passing through single height floor possible.

[cymonsgames]

N @ & a Q N

N N

A

(11 spaces between the 'N's on the lower level.)

1. In the map above put a portal below and above the box.
2. Step into the looping box. If you are not in the portal block step out and step back in.
3. Notice you're in the bottom portal right now, tho there's a duplicate of you in the upper portal.
4. Press up so that your aim goes up.
5. Fall through floor.

I had to solve a similar issue with side walls but I guess I never fixed it with floors and ceilings because you never stop in the floor... well, I guess now you do. I don't remember how I solved it tho, that was a long time ago.

[zorun]

This issue is present in the 1.2c version, so it isn't caused by any recent modification.

As for side walls, it is sometimes possible to stay just inside a portal. Don't know if it is a known feature or a bug, but it helps for some levels (this allow you to build a kind of "portal ladder" to climb up)