[SOLVED] Odd effects when 'CSS: Compress' = 'Yes'

I've installed the new css.php file. so it helped with bringing back spaces after comma's.
but it also gives a new thing: every page- or post load, show for a part of a second also a partial black screen. first the post/page is loaded, and then the partial black screen followes. same effect when I set Compress to "no".
how come?