Effect/Lens/Export/PNG/Transparency problem

Hi to all,

The easiest way for me to describe the problem:

1. I made rectangle, with green fill color

2. I made another, larger, rectangle with no fill color, which includes more than half of the previous rectangle

3. I applied e.g. Fish Eye Lens Effect to rectangle 2

4. I open PNG export window and there is no transparency outside green rectangle and within larger "fisheyed" rectangle

Is it CorelDRAW bug or how I can solve this?