Main form double buffered

Hi fooks,
I have a form with a vertical TSplitter on it, with a Right-aligned TPanel
and a Client-aligned TPanel. When I set "Form1.DoubleBuffered := true" then
the speed of  updating the screen is as expected, _only_ when the form is
Normalized (it refreshes about 20 times /sec).
If the form is Maximized, however, the speed is reduced to approximatly one
refresh per second. I _hate_ this happening, cause I dont have an
explanation for this.
Who can help me?