title: OnRender not called after InvalidateVisual()
body: <p>A custom WPF Control overrides OnRender. The method generates and displays a Path from custom data. The data provider is bound using a Dependency Property. The Dependency Property registers for an event when data changed. This event in turn calls InvalidateVisual().</p>
  
  <p>However, after the InvalidateVisual() the OnRender is not always called. </p>
  
  <p>We use the Prism Framework and the Region functionallity. The Control in question is embedded in such a Region, which is activated and deactivated. However, the Control's property "IsVisible" is true whenever the region is active. But still, when calling InvalidateVisual() the OnRender method is not called...</p>
  
  <p>What could prevent the OnRender method from being called?</p>