Need help on this weird sector effect

[Kef Nukem]

I need a little bit of help here. Everyone knows the map cranium I think (a.k.a Clearwater). It had this sectors beaming to another one which was behind the first one so:

|---|---|
| 1| 2 |
|---|---|

He did not just put normal sectors behind eachother but you can only see 2 lines of this sector if you select it. It's the same as when you create a block and move a block of the same size into the first block, then you get this "weird sector" too.
I've tried to make this like Billy Boy did but man, I'm stucked and I really want to know how it works because it can get very useful in my map.
Can anyone help me with this or do you guys have the same problem as me ?

[NutWrench]

Sounds like a double-stamped sector, which is usually a bad thing. What do these sectors do?

[Kef Nukem]

Nope, in this map it's not a bad thing. Although I dont know if it's double stamped since I dont know how to do it (or do you mean, first stamp a sector and then but over an other sector with the same size? ) Anyway the map can be downloaded here:
http://dl.fileplanet.com/dl/dl.asp?PlanetDuke/msdn/cranium.zip

And really, if you haven't played this before and dont know the effecst either, you will be confused. The effect I'm talking about can be found in:
- The building with the roof on it which you can just enter.
- The crane, the place where you can look outside of the crane.
- The turret behind this life guard tire.
- The hall at the end of the map.

[Kef Nukem]

I already found it out a little myself but still I dont know how it works exactly. Doesn't anyone know how this works?