I see no bug.In more details:
First, you have 40 HP, a 7/3 Golem grows to 9/5, and is not blocked, because 5 is not higher than 5, the other Golem gets +2 HP, so it has 7 and is blocked, because 7HP > 5HP 9+15(Dragon)=24. 40 HP -24 HP =16 HP. Your 16HP image.
Then, the Golem doesn´t grow (maybe clever AI, but why did the AI do that, before ? ), the 9/5 golem attacks you: 16-9=7 and then, the dragons kill you. Totally normal.