CorelDraw Graphics Suite X5 Power Trace

The white lines appear because of screen anti-aliasing and should not affect printing.
Unfortunately though, they may be visible when converting to a bitmap.
One workaround when converting, is to create one or two duplicates of all objects.
Select all, use the "+" sign on numeric keypad once or twice, then select all and convert.
Not what we want but at least it is a way around it.

In Powertrace there is also an option (may have been introduced in X6, don't remember) that makes object overlap instead of meet edge to edge. It is called "Remove object overlap" and should be left unchecked.