isModified always returns false if apply a validator to the QLineEdit and if the validator changes the text

If the following validator is set to the QLineEdit, isModified always return false.

Here is the validator can be used to reproduce the problem:
class UpperValidator : public QValidator
{
public:
UpperValidator(QObject * parent) : QValidator(parent) {};
~UpperValidator() {};
virtual State validate ( QString & input, int & pos ) const
{
input = input.toUpper();
return Acceptable;
};
};