ComboBox internal state not consistent when inserting at SelectedIndex and IsHandleCreated == false

• .NET Core Version: 6.0.101

• Have you experienced this same bug with .NET Framework?: Yes

Problem description:

Add items to the ComboBox and select one:

comboBox1.Items.Add("Item 1");
comboBox1.Items.Add("Item 2");
comboBox1.Items.Add("Item 3");

comboBox1.SelectedIndex = 1;

Now insert at the selected index: comboBox1.Items.Insert(1, "Test");

If the handle has been created:

• Item will be inserted into collection
• SelectedIndex will increment
• SelectedItem and Text remain consistent

If the handle has not been created:

• Item will be inserted into collection
• SelectedIndex will remain the same
• SelectedItem will be the newly inserted item
• Text will match the old SelectedItem

Issue discovered while adding events to Items collection (#6673)

Expected behavior:

• Internal state of control should remain consistent
• Behavior when handle has not yet been created should match that of when it has been

Minimal repro:

• Create new WinForms project
• Add the following to Main just after ApplicationConfiguration.Initialize();

var comboBox = new ComboBox();

comboBox.Items.Add("Item 1");
comboBox.Items.Add("Item 2");
comboBox.Items.Add("Item 3");
comboBox.SelectedIndex = 1;

comboBox.Items.Insert(1, "Test");

• Set a breakpoint on comboBox.Items.Insert(1, "Test");
• Observe the values of SelectedIndex, SelectedItem and Text before and after that line executes