[Jach]

Where's the design? (To me TDD was always championed to help specifically with Design as much as the vague Development. When using the vague Development too loosely you run into a recursive problem because writing tests is itself development so do you use TDD for your tests?)

Depending on how seriously you take the step of writing a unit test that reproduces the bug, you may be forced to refactor quite a lot of code to get that buggy section under test. Writing the test first can help guide your refactoring to avoid mocking the runtime world. But you're not designing anything, and it was all driven by the bug report.

[bluGill]

If you are that strict on your definition, yes you cannot TDD when fixing a bug. However all TDD advocates will tell you to write the test for the bug before fixing it. If the code was designed with TDD you will not have to refactor the code to write the test (though the test might be much bigger than it would need to be if the code was designed different). You seem to be describing working with legacy code though, not which is a different situation from TDD.