When creating a new CDockWidget it very briefly opens up as a floating widget. I observed this when I upgrade to v3.6 in one of my applications but am also able to reproduce it with one of the included examples.

Setup

Windows 10
MSVC 2019
Qt 5.15
Advanced Docking System (v3.6 and HEAD at time of issue 48c4106)

Steps to reproduce

1. Run the deleteonclose example.
2. Use either of the menu options to create a new docked widget.
3. Observe there is a quick window that opens and closes. I am assuming it is showing it as floating briefly.

Recording...I have slowed it down a bit but you can see a flash at the top left of the main window.