Install with default options, launch QtCreator and open one of the designer examples, for example designer/containerextension. Build fails with error message:
fatal error: 'QtUiPlugin/QDesignerExportWidget' file not found
Same happends with following examples (all try to include #include <QtUiPlugin/QDesignerCustomWidgetInterface>):
(calculatorbuilder, calclatorform and worldtimeclockbuilder examples work fine)
containerextension example tested also on Ubuntu14.04, works fine there.