Auto-completion broken for objects dragged into ui files

Steps to reproduce:

• create a Qt Widget Application from New Project wizard
• open the ui file (Designer)
• drag a QPushButton into the main window
• switch back to mainwindow.cpp
• go to constructor of MainWindow, eol of 'ui->setupUi(this);' and hit return
• type

  ui.
  

Current behavior:

• no auto completion for added objects ('pushButton' is missing) - applies for all other objects dragged into mainwindow as well

Note: former version(s) of Creator supported the auto completion for objects that have been added to the ui file via the Designer, seems to be a regression from Creator 2.8