As far as I understand you are using a Pane outside of the Docking which is not supported scenario. In order to have a fully functional Docking you should stick to the required structure of the elements inside as shown below:
Docking -> SplitContainer -> PaneGroup -> Pane
For more details about the Panes you can check the following article from our online help documentation:
If you have any other questions let us know.
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