 <p>Fabio, you were right about _Click eventhandler. But it did not solve my problem. My problem are causing groupboxes on my winform. Why, I don't know. This is my workaround for <strong>CheckStateChanged</strong> event that works like charm:</p> <pre><code> private void My_checkBox_CheckStateChanged(object sender, EventArgs e) { if (_addnew == true) { CheckBox my_cb = (CheckBox)sender; if ((my_cb.CheckState == CheckState.Indeterminate) &amp;&amp; (my_cb.Text == "Da")) { my_cb.Checked = false; my_cb.Text = "Ne"; } } } </code></pre>