Ever seen a quick fix turning out to create a chaotic situation, thats called Story of a Side Effect. Happens a lot in maintainence projects when you are looking for a quick fix, inspite of reviews and testing rounds, you still manage to introduce new bugs.
I really feel for a team to prevent any side effects to creep in, testing done by testing team can never be enough. Their skills can make them look for bugs in other scenarios of the same module, however, only a developer exactly knows whether or not there is a shared code between modules and changing anything in one module can lead to affecting what all other modules. On the other hand, due to the mindset of a developers, they only test the code on the same patterns that they wrote it on (dont think many would be able to understand this sentence). The best way to capture side effect, therefore, is to have the developer point out the parts of applications to the testing team that the testing team should surely test thoroughly to get the best out of both skills.
PS – May be I have left some related point untouched in this blog, do make sure to point out that side effect to me.