It is not at all uncommon for an activity to be scheduled for one activity type and clear it with another activity type. This is important when running the History List to report how one's time was spent.
It would be nice that when we clear the activity we have the option to change the type from To Do to Call for example.
Now I have two options to fix this:
Double click on on the activity and change type, save it, then clear it
Clear it and double click on the history entry to make the type changes there.