There is a lot of stuff that can make you crazy while you're working with UnrealEd. Some of those things are inherited from previous instalments, others are brand new developed for you to spice up this particular version. This article will be slowly updated to contain more and more things you should avoid.
Subtractive level + setting brush to be "first" in Order
Unreal3 Engine is additive only now. Subtractive level is only a curse cast upon us - an illusion created by one big blue brush encompassing the whole space and so making it solid mass. But this brush is first in order. When you want to send some (typically subtractive) brush to be the first it will be then beaten by this big additive brush (which will become second in the list then). So the rule is don't forget to send big-blue-brush at first again.