It certainly sounds like you missed or misunderstood something...
Can you tell us more about the impact on the earlier sub releases?
Where did that "considerable QA effort" come from?
Did you practice continuous integration? Automated acceptance and
unit testing?
The soul is dyed the color of its thoughts. Think only on those things that are in line with your principles and can bear the light of day. The content of your character is your choice. Day by day, what you do is who you become. Your integrity is your destiny - it is the light that guides your way. - Heraclitus