We hear this so often from our customers but haven't found this suggestion posted yet.
Another Act! Preference should take care of it. Just an option to automatically clear the contents of the Keyword search at the top of the History and Notes tab in contact detail when they navigate out of that record. Users frequently need to find a keyword within a contact but when they leave the record that keyword search remains, hiding all the next contacts' details.
Sometimes it's the simple things so hopefully this can be adopted into v.21.