Winform Combobox Databinding problem. Is this a bug or normal operation?

Question

Hi, I have a question. I am using the standard winform ComboBox who's text value is databound to my bindingsource. Everything seems to work correctly however, if I have the style of the combobox set to DropDownList and I change the value of the control by tabing over to it and then using the up/down arrow keys then the new value within the combobox does NOT get sent to the datasource, if however I click on the control and change the value using the mouse then the change makes it to the datasource, if I then change the property of the comboboxex to dropdown it seems to save the change to the datasource regardless if I tab and change the value using the up or down arrows or change it with the mouse.. Any Help would be greatly appreciated. Is this normal operation or a bug? Thanks,