Qt Designer integration does not automatically add required modules to project

I use QTCreator to create a qtgui app:

• File -> New File or Project -> Qt Gui Application
• I create a new project "qtgui"
• I open the geraraten mainswindow.ui in the designer
• I add a QWebView Widget by drag and drop (ObjectName property = webView)
• I set the webView Widget url property to:
  url = http://www.google.de
• Hey fine: I see the google site live in the QTCreator designer.
  Appearently It can access the google website

So I try to build it and get the following error:

/home/.../qtgui-build-Desktop_Qt_5_0_1_GCC_64bit-Debug/ui_mainwindow.h:44:
Error:undefined reference to `QWebView::QWebView(QWidget*)’

/home/.../qtgui-build-Desktop_Qt_5_0_1_GCC_64bit-Debug/ui_mainwindow.h:48:
Error:undefined reference to `QWebView::setUrl(QUrl const&)’

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I downloaded qt 5.0.1, installed it just now to give it a try,
3 minutes later I got the first showstopper again,
which lets me think its a beta version.
(even if I like Qt but didn't have the oportunity to wor with it)