FIX: The validating event on the user control does not fire as expected (810852)

MORE INFORMATION

Steps to reproduce the behavior

1. Create a Microsoft Windows Forms application that has two user controls, the UserControl1 user control and the UserControl2 user control. The UserControl1 user control contains a Tab control that has two tab pages. The TabPage2 tab page contains the UserControl2 user control. The UserControl2 user control contains a TextBox control.
2. Paste the following code in the Validating event of the TextBox control:

   if ( textBox1.Text.ToLower().IndexOf("a") != -1 )
    {
    		MessageBox.Show("Invalid entry. Reenter data again.");
    		e.Cancel = true;
    }
    else
    {
    		e.Cancel = false;
    }
    

3. In the expected behavior, you type the letter A in the text box on the TabPage2 tab page, and then the e.Cancel property is set to true. This prevents you from switching to the TabPage1 tab page because the validation has failed.
   
   However, the bug permits you to switch to the TabPage1 tab page. When you switch to the TabPage1 tab page, the e.Cancel property resets to true. Now you cannot switch back to the TabPage2 tab page.
   • If you replace the UserControl2 user control with a simple TextBox control on the TabPage2 tab page, the Validating event and the e.Cancel property work as expected.
   • If you replace the UserControl1 user control with a simple Tab control that has two tab pages on the form, and you put the UserControl2 user control on the TabPage2 tab page, the Validating event and the e.Cancel property work as expected.
   To reproduce the problem, you must have either the UserControl1 user control or the UserControl2 user control involved, or you must have both the UserControl1 user control and the UserControl2 user control involved.