Debugger pretends to allow editing fields in locals & expressions view but often doesn't

Take for example this:

#include <QDebug>

int main(int argc, char *argv[])
{
    QString b("lalalal");
    qDebug() << b;
}

Break on the qDebug() line and double click on the value of b in the l&e view. You get the edit field, you can change the value, but pressing enter reverts it to the previous state.

I understand that not all debugger engines support editing of all data types. However, as it is now, nobody knows under which circumstances editing is actually supported and therefore this feature is a constant source of frustration. The edit field should not pop up in the first place if the value is readonly.