After the widget has been disabled and Enabled, QLineEdit on this widget can not be edited.
This is very much limited to Mac and cocoa. It works great with carbon.
Git bisect points to Align merge as faulty commit.(72aa2eb43b0cf5a6eef940da05ac58f605794ffb)
can be reproduced with this tiny code.

int main(int argc, char** argv)
{
    QApplication app(argc, argv);
    QWidget w;
    QLineEdit *lineEdit = new QLineEdit(&w);
    w.show();
    w.setEnabled(false);
    w.setEnabled(true);
    app.exec();
    return 0;
}