[Qt-interest] Qt Creator 1.3.83 QML error

[OS Prog]

Hi,

I'm trying the examples and demos for the QML in Qt 4.7b. When I open
the calculator.qml from calculator demo and go to the design I have a
message "Internal error()" and the design is not allowed.
If I remove property "operation" from the "CalcButton" all goes fine
(apart of the operation was not set).
What could be the reason for this error?

Regards,
Nik