The Paste (Ctrl+V) command can be trapped under the EVENT_VAL_CHANGED case.
You could track if there has been a keypress event (that implies some manual modification on the control) and swallow the val_changed event not preceded by such type of user operation on the control (keypress is fired before the val_changed event).
In event_keypress case you could raise a flag in case of an alphanumeric character an test the value of the flag in the event_val_changed case. The flag should be reset on event_got_focus.