When assigning value make sure comboBox stick to the value assigned instead of selecting from its list. Even if value is same but only differ in case.

Like

If I write comboSub.Text = "BlowMolding";

and comboSub list items are blowmolding,

                                                     injectionmolding etc.

Still comboSub value should stick to BlowMolding and should not automatically convert to blowmolding from the list.