I have finally found what is the problem with my first map "Pipeline". 

**Shanty 05** found under   Utilities > Fences

Whenever you use this piece in a manner besides fencing, ex: roofing; your point of view must remain below it for it to appear normal.  If you have a point of view that is above it, it will then make many other objects invisible.  This glitch can be quite annoying.

I haven't played my Pipeline level much because of this glitch.  Now I will remove all of this item and use another fencing to complete the level.  Coming kinda soon!!  "CoD4:Pipeline 3.0"