I have noticed that when playing rebuy tournaments with addons HM3 picks up the fact that I have had the addon, but does not pick up the amount. So in the Tournament Editor, Results section, it says 'Addon amount: £0.00' and 'Number of Addons: 1'. I therefore have to manually enter the addon amount.
The rebuy amount is picked up correctly.
I am using v.3.1.15.0, and have only played rebuys on Poker Stars so can't say if this affects all sites.