This is reproducible in my app. If I undock two dock panels, then drag them to combine them into a single floating dock panel (tabbed), the dock zone "stencil" does not appear if I try to re-dock that floating panel back into my main form docksite. If I then undock one of the tabbed dockpanels from that floating docksite it then shows the dock zones, but not always (I sometimes have to drop the dock panel and start dragging a 2nd time). But at least I can eventually get them both back onto the main form's docksite.
What would prevent the dock zones from appearing?
LMD Tools 2019.11