title: Qt Creator can't display form, but Qt Designer can
body: <p>Using fedora 21, cmake, Qt Creator 3.3.0, Qt Designer 4.8.6</p>
  
  <p>Have three forms in Qt project, two display fine in the form designer, but for the third form only the menu displays, but no widgets.  Trying to add new widgets to this "blank" form results in a forbidden / no-entry mouse cursor and the widget cannot be added.
  <img src="https://i.stack.imgur.com/PEBmQ.png" alt="Blank form in Qt Creator">
  Opening the same form in Qt Designer, has the form displayed as expected.
  <img src="https://i.stack.imgur.com/xb9ve.png" alt="Same form displayed correctly in Qt Designer">
  Tried without success: removing and reinstalling Qt; moving from Qt 5.3 to Qt 5.4, moving the code to another computer, deleting the cmake build folder, moving the project code to a new folder and recreating the project, following the google advice to add modify xorg.conf, switching between Gnome Shell and Gnome Wayland.</p>
  
  <p>This feels silly, but any guidance appreciated.</p>