TextEdit demos qt item menu not clickable

The first time I saw this.
I was playing around demos in the Qt SDK. And I tried textedit. For some drak reasons the first two items menus, File and Edit, are not clickable, while the next are. Also, if I firs click on the last items and then move the mouse back to the first item menu I can use the menu items.
Why??? I read the code and it seems standard Qt code.
Regards

More weird. I discovered that if I click the Alt button than the menu items become enabled and clickable.

I discovered my error. I was putting a background widget in the mainwindow. Solved.