The dropdown option for a combo box can only be shown when the combo box has
the focus. Thus, I don't understand your statement that you can scroll
through the combo box list but that the combo box doesn't have the focus
until an item is selected. In order to scroll through the list, the combo
box must have the focus.
Your statement about how, after an item is selected, the cursor ends up in
another control, suggests to me that you have code running on the
AfterUpdate event of the combo box that is moving the focus from the combo
box to the other control. I think you have code running here than what
you've posted so far.
Your solution to use the OnEnter event for the showing the dropdown list is
ok; alternatively, you can use the OnGotFocus event (which probably would be
my choice) to do the same thing. The OnChange event occurrs whenever a
character is typed into the control or an item is selected from the dropdown
list (or from a listbox's list). As such, it's used for special things when
you want to examine each character or when something else needs to occur as
soon as the control's contents are "dirtied".
If you open the module behind the form, there likely is more code that is
running on various events. If you can post that, perhaps we can figure out
exactly what is happening in this "wayward" form.