I've been using TurboCAD Deluxe 19 and didn't have this problem. I often use a polygon to hide objects within my drawings. I set the polygon properties to the Solid White hatch (just below None), then Pattern Color to WHITE, and then Convert Color in "Accordance with a Current Background Color" to NO. Then I click OK.
With the Polygon still selected, I go to the Line Pattern rectangle above the drawing and select No Line (the 10th selection from the top). In TurboCAD Deluxe this gives me a white object with no outline that if bought to the front and place over any part of the drawing will make that part of the drawing disappear.
(The attached is an example of a door I've inserted in an existing wall and the black rectangle should be line-less and white, blocking out that segment of the wall.)
I hope this is clear, turns out to be harder to explain than to do.
I have found this to be very helpful, especially when blanking out sections of a wall for door or window placements when incorporated in door or window blocks.
Now the problem with LTE Pro 5 is when I select White for the Pattern Color, it actually turn out to be Black in the drawing, just as if I had selected Black to start with. Works with Deluxe, but not Pro 5.