Main menu of Qt apps locally integrated in the window title bar disappears after activation of any menu item

[Alexey Kulik]

[The bug]
When the integration of the app menus into the window title bars is turned on, call of any dialogue from the menu leads to disappearance of the menu. After that, the window title bar displays only the application title string. The main menu cannot be seen and cannot be accessed until you switch to another application and then return. The bug is observed only for unmaximized windows. The main menu of maximized windows works fine.
This bug is observed only for Qt applications. I have “succeeded” to reproduce it for VLC, Gwenview, digiKam, Krita, Calliga, VirtualBox, GoldenDict, Mixx.

[How to reproduce]
1. Make sure that “Show the menus for a window” parameter (System Settings -> Appearance -> Behavior) is set to “In the window's title bar”.
2. Start any Qt application, say, one of mentioned above. Let it be, for example, Gwenview.
3. Unmaximize the app window.
4. Activate any dialogue from the main menu. For instance, File -> Open... or Settings -> Configure Gwenview...
5. Press Cancel to close the dialogue.
6. Hover the mouse pointer over the window title bar.

[What is expected]
The app menu should appear and be accessible.

[What happens]
The app menu is not shown. Only the application title is displayed in the title bar.

The following screencast shows the bug “in action”:
http://www.youtube.com/watch?v=WAfJXmwDJpg&feature=youtu.be

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: unity 7.2.0+14.04.20140416-0ubuntu1
ProcVersionSignature: Ubuntu 3.13.0-24.46-generic 3.13.9
Uname: Linux 3.13.0-24-generic x86_64
ApportVersion: 2.14.1-0ubuntu3
Architecture: amd64
CompizPlugins: [core,composite,opengl,compiztoolbox,imgjpeg,decor,snap,move,gnomecompat,imgpng,vpswitch,place,grid,resize,text,imgsvg,unitymtgrabhandles,regex,mousepoll,session,wall,animation,fade,expo,workarounds,scale,ezoom,unityshell]
CurrentDesktop: Unity
Date: Fri Apr 25 22:38:19 2014
InstallationDate: Installed on 2012-05-02 (723 days ago)
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120425)
SourcePackage: unity
UpgradeStatus: Upgraded to trusty on 2014-04-21 (3 days ago)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Tamir (sugip)]

Also have to mixx.

[GrandVizier (grandvizier)]

Also affects octave 3.8.1 GUI window and lyx 2.1, making them very difficult to use.

[Benjamin Xiao (ben-r-xiao)]

Also happens with Mumble. When is this bug going to be fixed? This makes LIM unusable for all Qt apps.

[Mateusz Stachowski (stachowski-mateusz)]

This bug is resolved in Vivid the current development release.

Also this should be marked as duplicate of Bug #1312137 even if that bug has less people affected because it has target assigned for the next Trusty SRU and this one doesn't.