Problem with docking in MDI applications

Hello.

I am facing a problem with the displaying of docking panes within an MDI based application. When you dock at the top or anywhere else and afterwards drag the border of the frame towards the end in order to get it all displayed, there is always a small zone of the screen left in that direction, and it seems not to be able to cover completely this area. We have noticed that problem even on Codejock´s examples as you can show in MDIPanes. I attach a screen capture of this problem on MDIPanes example.

As you can see, that white zone at the bottom cannot be eliminated by dragging along.

Is this normal or there is any parameter and/or feature to get it?

Thank you very much for your help.