@MikeMason, @ddljohn-- We're learning about language and perception in one of my classes right now. And what you guys are describing sounds like the "Freudian slip." theory. This is where information processing in the brain goes wrong for a minute and causes the person to use a word different than what they meant to use. We usually call this "slip of the tongue".
I think this theory shows that someone's perceptions and knowledge of language means little if there is a fault in the information processing part of it.
The person who can't make the right connection between language and perception can be seen in an unfavorable way. Sometimes people think that this person is doing it on purpose because the slip of the tongue doesn't happen constantly. But in fact, it's not their fault.