OK - a challenge for Photofiltre

I used their source picture, and made a selection using polygon. Then I inverted the selection - I wanted to drop the black shadow inside the brown part (see below). The option was not available ...arrgh.
The solution to this problem: I filled the brown box with a color and I made a new selection of the color by the magic wand. I undoed to remove the filling color and inverted the selection (to get the same as above) and the menu to drop shadow appeared .. I am confused
Is it a bug or did I something wrong?
Here is the result - the problem was with the inner black shadow http://photofiltre.suewebik.net/galerie ... ge-try.jpg