Take a comboBox, make the drop down appear. Then press the left button of your mouse on an item. Then drag to another item in the list and release the mouse button. You see that the item you released your mouse on is not selected.

I took a look here : https://wiki.openjdk.java.net/display/OpenJFX/ComboBox+User+Experience+Documentation especially in 3.2 Detailed Behavior and it says:
"User confirms a selection in the dropdown list by mouse click or by dragging from the drop-down arrow to the selection and releasing the mouse button."

The second part of the affirmation is not working (see https://javafx-jira.kenai.com/browse/RT-25371 ). And the first specify a "click". So does click means mousePressed or mouseReleased? Or both?

Anyway, in every dropdown list in windows, what I described is the normal behavior.