Hi Georgi,
You could use the SetDockVisibility statement in the NewDockStateEndLoad event. Designer dockstate will load after the form load event. So If you change any visibility or dockingstyle for the docking windows in form constructor, it will not affect the docking windows. So NewDockStateEnd Load event is the right place to modify the docking window at the application startup.
I have modified your sample and attached with this response. Please take a look at this sample and let me know if this is helps you.
Thanks for using Syncfusion Products.
Regards,
Vijay
DockingProblem.zip