In WebDirect as I understand it, loads first the theme of a layout with its default values and then applies local layout styles.
This caused some flicker for me in the past, so if you have a local style applied on your portal that might be it? Just an idea
I'm using the Enlighted Theme, which has been extensively modified. The entire solution uses the same theme.
Not sure that is the cause.
Highly recommended web direct optimization video
Good article about themes