Yep, it works now.
I unchecked "Always use the QML emulation layer provided by Qt Creator". After that, QtDesigner built a new and working qml2puppet layer. Thank you very much, again!
Greetings to Berlin,
Frime
The problem can be solved building GDB with a Python 2.7 or 3 in path. Python 2.6 from Centos 6.X lacks some feature which breaks the debugger integration for Qt Creator 3.1.2.
Python 2.6 could also break the debugger pretty printers for Qt Creator > 2.8.1 and < 3.2, but I haven't tested any other version than 2.8.1 and 3.1.2.
More info in can be found in QTCREATORBUG-13462.