CorelDRAW front minus back problem

I am wondering if anyone would have a solution to this problem:

I am simply trying to combine objects and "knock-out" certain areas in a design but when I do so, the area that should be getting knocked out just fills in solid.

This is hard to explain...   I tried to upload a file that I am having issues with but it is apparently larger than the size I can upload.

This has been happening with corel X6 and corel X7.    It can be very frustrating and it really slows us down.

Any help is appreciated

John