Qt Creator's menu bar disappears when UI editor has Menubar item

After opening ui editor (doubleclick .ui file) Qt Creator's menu bar completely disappears if there is a menubar object in list. Switching window does not revive the bar, only restarting QT Creator does.

I attached project and screenshots

To reproduce bug
1) open attached project
2) open "mainwindow.ui" by doubleclicking
3) try to access menu (screenshot 2)
4) remove menubar from object list
5) restart qtcreator
6) do steps 1,2,3 and observe the menubar in place (screenshot 1)