That's not the wrong count. It works in order of the creatures on the bored. In the end it all equals the correct final amount.
That is provided when the healing creature attacks, they aren't at full health. The healing creature will heal, and then the attacking creature will attack. So a person at 50hp gets hit for 1, -5, and 2. It will go from 50 to 49 to 54 to 52.