With the default DragDropMode whenever pane is dragged, its content is being removed from the current visual tree and placed inside a Window, so this operation with a lot of UI might cause delay.
As for the Deferred mode issue - we are not aware of it. Can you please provide sample project that reproduces it, so we can check it on our side?
Basically if you provide sample project - we will investigate both of the cases and improve the control. Using the Deferred DragDropMode seems to be best solution here, so we would be glad to resolve the issue and allow you to use the feature.
I'm looking forward to hearing from you.
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