A nice way to fix bugs is to make the buggy state impossible to represent. In cases where a bug was caused by some fundamental flaw in the original design, a redesign might be the only way to feel reasonably confident about the fix.

Oh, that's because a bug in requirements or specification is usually a killer.

I have encountered areas where the basic design was wrong (often comes from rushing in, before taking the time to think things through, all the way).

In these cases, we can either kludge a patch, or go back and make sure the design is fixed.

The longer I've been working, the less often I need to go back and fix a busted design.