Combobox Highlight Text

Combobox Highlight Text

I'm having a problem with regards on the behavior of ComboBox,the
following is the Properties of my comboBox
Combo.AutoCompleteMode = SuggestAppend;
Combo.AutoCompleteSource = ListItems;
The the weird behavior is when i type some text in the comboBox, and of
course since SuggestAppend was set in the AutoCompleteMode, ComboBox
automatically give some hint. It occurs if the item were selected using
keyboard(arrowdown).

but when i alreadly leave the comboBox, The selected items from the
comboBox is still highlight.

as you can see, the Caret is already on the "Department" Field and the
"Payee" selected item is still highlight.
Please give some advice on how can i workaround this weird behavior.
Thanks in advance.