QDockWidgets disappear if their window has been minimized on Mac

A dock widget disappears completely on Mac if its main window is minimized, unminimized and the dock widget is docked back. Instead of docking, the dock widget disappears. Setting visibility to false/true does not bring it back. Here's steps how to produce in the Qt example examples/widgets/mainwindows/dockwidgets

1. Undock Customers and Paragraphs
2. Minimize the main window (minus sign on the title bar)
3. Open the main window back to be visible
4. Dock Customers and Paragraphs (drag them or double click their title bar)
5. The dock widgets disappear and the View menu does not bring them back

This may be related to Qt Bug QTBUG-31503 Floating QDockWidget not minimizing with application

The dock widgets do not disappear in Qt 4.7.4 on Mac. This is new behavior in Qt 5.1.0 beta.