Hi Frank,
Thanks for your interests in Syncfusion products
We could not able to reproduce your mentioned issue. Instead we have create a simple sample which demonstrates the dynamic adding of the children element to the Docking Manager control and dynamically removing its added children. Kindly download the sample from the below mentioned location.
http://files.syncfusion.com/support/Tools.WPF/7.1.0.30/Tools-WPF-Forum/Docking/main.htmPlease let us know if you have any queries.
Regards,
Bala.