QtQuick Designer refuses to work

Here's what I did:

• Open all files in $CREATORDIR/tests/manual/qml/testfiles/testfiles.qmlproject
• choose a Qt 5.3.1 kit
• open states.qml
• switch to "Design" mode

What happened:

• everytime I switch to the Quick designer a message box tells me "The executable of the QML emulation layer (QML puppet) may not be responding. Switching to another kit might help."