Why so many regressions?

[andreas84]

normally when one bug was fixed i would expect it to stay fixed and not come back. Why do so many bugs come back?

[Black_Fox]

Regression isn't a bug that came back, it's a bug that wasn't here before.

[vicmarcal]

Yeah, regressions can happen because a lot of different reasons.
Just to show a listbox with content inside, there are more than 100 "functions" related.And So if one of them becomes bugged, the listbox regresses. Our testman tries to control this potential regressions through more than 10 million of tests(not joking) but we need much more tests to discover all the small regressions.
We can have regressions because our MM rewrites, because Wine introduced a new bug while fixing tons of others,etc. The best part is that each Regression has a reason: We can find the commit that caused the regression and hence we can discover why it appeared which makes easier to find a solution.

[SomeGuy]

In many cases different root causes can create what visibly looks like the same problem.

[Z98]

Or, you know, we had hacked something to work previously and now that some underlying assumption has changed due to a correct implementation, the hack no longer works.