QButtonGroup::checkedId () outputs uncommon result

I have 3 RadioButtons within a groupbox. Then I create a QButtonGroup which consist those RBs. when I execute below code I got result as -2 ,-3 , -4 according to the checked button. qDebug() << "ID of checked Radio Button" << ui->my_button_group->checkedId(); How it is possible? According to the Qt help checkedId() returns checked radiobutton id within group. if not checked any rb then it will be -1. Thanks in advance.