You can either say 'I changed my mind' or 'I had a change of heart'. The two expressions mean the same thing, but you can't mix them up. That's why 'they had a complete change of mind' was marked wrong. You can change your mind, but you can't 'have a change of mind'. This is the problem with idioms - you need to get the wording exactly right.

Emma: The differences are almost cryptic, but are certainly, metaphysical. The government can be said to have a mind, because Government Policies and Laws can be said to be epressions of THOUGHT, whereas they are not expressions of FEELING. Heart is a figure of speech, not fact. At the same time, Mind conceptions derive from philosophical Dualism, which is now competing with the materialistic philosophy of Monism. The difference being that Mind is Supernatural, whereas Brain, as a substitute for Mind, is Natural. What makes Mind and Heart seem to be equivalent, is that both are viable conceptions from Dualist Philosophy, which says that reality consists of a Mind/Body combination of the Natural and Supernatural. Metaphysically, Mind and Heart are more or less equivalent, Even though in Metaphysics, we can point out the distinct difference. In the end, as your other respondent's show, it reduces to "Figures of Speech" rather than Legal Fact.

It sounds like you took a bad test. One could argue that "change of heart" is more about emotion than "change of mind", which strikes me as being more rational. Both have the same connotation (= word mood/feeling) and the same basic meaning in English.

As far as I'm aware a change of heart is simply a more emotionally considered decision than a change of mind. :)