[Reg 5.11.0->5.12] Menu of completer is not closed on application close

When completer menu is open and user closes the application, menu does not get closed and program still in running state

Steps to reproduce:

1.Build and execute the attached sample code.
2.Enter "J" into the Country field.
3.Click the close button in the title bar.
4.The menu of completer is left alone.
5.Click outside of window.
6.The menu disappears and the program is still running. 

Problem is seen only with 5.11.1 and Dev branch on MAC. Customer has seen same problem with 5.6 and 5.7 also. 

I have tested it on Windows also and it is working fine.