Blinking .swf when loading

Hi
I was working lately on this tutorial:
http://www.kirupa.com/developer/mx/preloader_transition.htm
and I wanted to make sth similar but a little more complicated (only in looks - not in code).
Its sth like this: I got a sheet of paper with loaded .swf file on it (same as in that tutorial); then the sheet wraps itself (the .swf file on it disapears because the sheet is a MASK); when it is wraped another .swf file is loaded (cannot be seen yet); and at the end the sheet unwraps and the new contet (new .swf) is revealed.

And I got this problem:
when the new .swf file is being loaded it appears for a half of a second (even if there is NO MASK on it - and it shouldn’t be seen!) before even the sheet begins to unwrap and then disapears and everything is going ok. No code errors.
Why do I have such effect of blinking on load ? It completely ruins the cool thing with wraping. Can you give me any advice ? There is no such thing in mentioned tutorial