Hello Ioannis Papasavvas,
Thank you for the question.
RadDock detects when a form is up to become an MDI child and takes it from the original MDIParent. Then, this form is hosted in a RadDock window. When these actions take place, the MDI relation is broken and the form is not a real MDI child anymore, so the MDIParent property becomes null. This is an expected and desired behavior.
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