Well, I never received any reply from the DSP Quattro folks for the bug reports I sent them, so I'm not going to bother to send more bugs as I discover them.
There are more bugs. I'll mention two in specific: when working with a Playlist, DSP Quattro does not detect unsaved changes when you close a playlist, and so you can accidentally lose data by either forgetting to explicitly save the playlist, or opening a second one, which results in closing the first one. Also, although you can specify a fade at the end of the last file in your playlist, DSP Quattro apparently does not save this information, so upon re-opening the playlist, the final fade type and duration are always lost.
This lack of responsiveness means I specifically _do not recommend_ DSP Quattro; in fact, I "un-recommend" it. It's a great program, and all programs have bugs, but I would not advocate that anyone pay $150 for an audio-editing program that is not actively supported by its developers.