- Throw ArgumentException in DockContainer.ReplaceChild if newChild is already in the container to avoid index shifting bugs. - Add comment in DockPanel.CheckCleanup explaining the asymmetric root panel collapse behavior.
- Throw ArgumentException in DockContainer.ReplaceChild if newChild is already in the container to avoid index shifting bugs. - Add comment in DockPanel.CheckCleanup explaining the asymmetric root panel collapse behavior.