Hello World for QtQuick2 does not compile with #include <QDeclarative/QDeclarative> when QML debugging is on

When you create a Hello World app for QtQuick 2 and include <QDeclarative/QDeclarative>, the program will not compile.

Build stops with compile errors:
/home/walter/Qt5.1.0/5.1.0-rc2/gcc/include/QtDeclarative/qdeclarativedebug.h:58: Fehler:conflicting declaration 'QDeclarativeDebuggingEnabler qmlEnableDebuggingHelper'

/home/walter/Qt5.1.0/5.1.0-rc2/gcc/include/QtQml/qqmldebug.h:59: Fehler:'qmlEnableDebuggingHelper' has a previous declaration as 'QQmlDebuggingEnabler qmlEnableDebuggingHelper'

Both declarations are conditional to the same define: QT_DECLARATIVE_DEBUG
When you unselect QML-Debugging on the Projects/Build page, The application will compile.