Maya Boolean Problems

Hi there.

I'm working on a a complex polygon that requires the use of the boolean
difference tool to make the elaborate shape.

The problem I'm having is not all of the shapes perform the operation properly.
Three of the shapes work just fine and leave a nice cut out behind. The rest of
the shapes either remove the main object from the scene, or both objects
disappear completely.

I've had this problem before and it always is a frustrating struggle that ended
up in scratching the shape or making it a much more complicated way.

I've tried deleting the construction history for all the objects as well as
using the Polygon>Cleanup option.

Any ideas why booleans give so much trouble?

or even more specifically...