WPF doesn't always repaint when using WindowsFormsHost

I have a simple application which is hosting a Managed DirectX Control using WindowsFormsHost. I've overridden the paint methods in the Control to prevent flicker:

protected override void OnPaint(PaintEventArgs e)
{
    if (this.Visible == true) { base.OnPaint(e); }
}

// Don't paint the background unless the control is not visible
protected override void OnPaintBackground(PaintEventArgs e)
{
    if (this.Visible == false) { base.OnPaintBackground(e); }
}

There is a timer which periodically invalidates the Managed DirectX Control so that it will be redrawn.

My problem is that when I lock the computer (WIN+L), and then unlock it, the WPF content around the WindowsFormsHost occasionally does not get fully painted. Various portions of it are not drawn until I drag the window completely out of view. Any ideas on why WPF doesn't finish repainting itself?

Apologies if this is too vague 开发者_C百科to solve the issue, I'm unable to share more source code.