I our project we’ve been fixing a lot of old bugs lately, and one would think that some of our debt should decrease.
Unfortunately, the “feature debt” increases correspondingly, since the amount of time we spend on fixing bugs (“paying bug debt”) results in less time spent on implementing new functionality.
Also, the bug fixes does not necessarily decrease our technical debt, depending on the type of “fix”.
What I feel is that there are several types of debt in a project, and the are all eating the same resources.
This would in my eyes be just one more reason for keeping your debt under control (close to zero), whether it is bug-, feature- or technical debt. Test early, test all, test automatically is my advice.