SendKeys “{TAB}” does not move focus to another control when ComboBoxEx is in focus

I have a question about your ComboBoxEx control;

I use the following code to let the program operator use the Return key to move between controls;

Private Sub Form1_KeyDown(Keycode As Integer, Shift As Integer)
   If KeyCode = vbKeyReturn Or KeyCode = vbKeyDown Then SendKeys "{TAB}"
End Sub 

It works fine with all the controls, but not with the ComboBoxEx control, is there something wrong with my code?

I also tried some other code, but it seems not to work.

This can be fixed by adding the same code to the ComboBoxEx control’s own KeyDown event. However, this indicates that there is some sort of issue with the focus handling, which I have not yet got to the bottom of.