OpenGL Display area doesn't match to GLControl under MacOs X.

My Winform application is composed of two panels.
The first one contains Buttons. The second, called DocumentsPanel, contains user control with OpenTK GLControl.
My Form has a padding of 10.

I designed a user control, that i used as template. This contains : a textarea, a button, a panel.

I create a user control called GLDocument, that heritates from my template. I add a GLControl in its panel.

I add GLDocument to my DocumentsPanel by code at runtime.

Under Windows and Linux there is no problem. But under MacOsX, the OpenGl drawing area doesn't match to GLControl.

This area is stick to the upper Left corner of my form. The GLControl is a its place inside my GLDocument, and itseems to be empty (white).

Is it a PointToScreen or PointToClient Bug ?