Found a work-around for this issue. First of all, Default Project.mpdp.ProjectData is a directory, not a file. Whenever an audio file is opened in Mixpad, 4 files are generated in this directory the first time the file is opened: (number starting at 0 and incrementing by one for each opened file).aud, .audioinfo, .grf and Recover.mpdp-recover. The last recover file (I believe) is used if there is a crash while working in the application for recovery purposes so as not to lose all work up to that point. The recover file disappears when Mixpad is closed regularly. Subsequent opening of the same audio file uses the .aud, .audioinfo and .grf files generated originally, if they are present and the original audio file opened has not been changed.
I think the only files that need to be kept are whatever files are associated with whatever is currently being worked on in an open Mixpad session. The other files can be deleted.
In my particular case, I was listening to files that are three hours long. I like to use Mixpad because I can recognize talking, commercials, public service announcements, weather reports etc. and skip over them. Generally, I listen to about an hour of each different show at a time. So to mark my place in the file without changing or saving it, I modify the original file name with @HH_MM_SS_DDD. That way I can re-open the file later, add a bookmark, click on the bookmark and play from that point on. The problem with that is Mixpad sees the file as a new file because of the different file name, and generates 4 new files every time I re-open the file. Once I’m finished listening to each three hour file, I delete it.
It might be better for me to use some other program besides Mixpad for what I’m doing, I’m not sure. Maybe WavePad, which I also have, though not sure it would be any better.