Faulty behaviour of QMenu in Unity

[krasnal]

Summary:
Once I clear and disable menu when I enable it again and try to add some actions those actions are not visible and some strange "Activate" entry is visible.

Description:
I'm using Ubuntu 16.04 (up to date) and Unity.
I'm developing an application that will have different "modes" and each mode needs to update the global menu.

When switching modes I do something like:
- clear menu
- add appropriate actions
- if there are no actions to be added then disable menu

I'm attaching very simple app with which you can reproduce the problem.
Procedure to reproduce and symptoms:
- start app
- change between "save" and "load" radios and observe if "Data" menu updates properly
- then select "no action" and observe that "Data" is not active as it should be
- then select back either "save" or "load" radio and observe that the menus are not restored properly
  (instead of normal save/load actions there appears "Activate" which does nothing).

The very same app works as expected on Windows and also on my Linux when running under awesome manager (so no integration of menu with window bar - which I happen to like :)).

Best regards
Andrzej