Hmm, well that is certainly strange! Thanks for bringing this to my attention. I'll be fixing this for the 3.9.22 update coming out in the next week or so.
If you'd like, it would be really helpful to me if you could send me your Data folder, so I can see what your tax settings are and how they are applied to your Projects.
Please look at this topic for more info: http://www.applesource.biz/supportboard-new/index.php?topic=15.0