Its a big misconception is that new features are the source of instability. In general this is not necessarily a fact.
Very often new features are isolated from other features or build upon existing infrastructure. As such any bugs arising manifest in the new feature itself and NOT in pre-existing features.
Even in the case of a complex integrated feature like patch points there were very few bugs that affected other areas of the application - and this was during its development prior to release.
On the other hand I find bug fixes to existing features relatively more likely to introduce unwanted side effects. We regression test the heck out of these bugs when necessary (unless its a trivial fix) but despite our best intentions sometimes problems do indeed crop up and its unavoidable. This is not specific to Cakewalk by any means - all software companies face the same issues.
Relatively speaking in our new model the bug to fix ratio is really small compared to before when we released much bigger updates. Whenever we release a new update all eyes are on it and people report any problems found even if they are not specific to that update, so it may appear more problematic than it actually is...