100% CPU-Load when double-buffering is activated with WS_EX_COMPOSITED

Question

To stop my application from flickering, I tried to activate DoubleBuffering for all of my controls and subcontrols.

To achieve this, I added the follwoing codesnippet in my mainform:

protected override CreateParams CreateParams
    {
        get
        {
            CreateParams cp = base.CreateParams;
            cp.ExStyle |= 0x02000000; //WS_EX_COMPOS

            return cp;
        }
    }

The problem is, that with WindowsXP the cpu-load becomes almost 100% and keeps up. No problem on Windows7.

It looks for me, as it is the very same problem as in this question. Is there a "easy" solution in C#? Or asked in a different way -> What usually causes this behaviour? So I can find out the problem in my application.

UPDATE: Maybe some more information to help you folks help me. What I am trying to do is showing a semi-transparent form ontop of the mainform with an progressbar. This "progressBarForm" is in a second thread to have this progressbar running. On Win7 everything works fine, as mentioned above with WinXP (.net4, activated desktoptheme) there is 100% cpu-load after the progressbar was shown once - also the acutal payload-function needs much longer to complete - maybe because of the high-cpu-load done by the progressbar. Where and what should I check again? Some ideas?

Btw.: I don't think the thread is a problem, as when I show the form in the mainthread and don't refresh anything, the result (high cpu-load) is the same...