Empty tax rate - shouldn't be able to add it

If you add empty tax rate in admin -> Locations / Taxes -> Tax Rates, without Tax Class Title, zone and everything else, it's stil added. That wouldn't be much of problem if I thing, this wouldn't couse double taxing. It also cannot be deleted from tax rates, because it's not shown in table. If you go to zone definitions after adding an empty tax rate, you can see there are two tax rates instead of one. Empty tax rate must be deleted manually from the tax_rates table in mysql.

Which version of Zen Cart ?

Zen Cart 1.3.5
Database Patch Level: 1.3.5
v1.3.5 [2006-09-11 20:21:45] (Fresh Installation)

How I did it... First I created tax zone, then I created tax rate without tax classs (no class existed yet), and after pushing insert button, no tax rate was displayed. Then I created tax class, and added new 20% tax rate for that class. After creating some articles, all of them had 40% tax added. I lost couple of hours trying to set propper settings in admin, without success. Then I noticed, there are two tax rates in admin/geo_zones.php (Number of Tax Rates: 2) for the existing tax zone. In admin/tax_rates.php there was only one tax rate of 20% shown. I looked up zen database with phpmyadmin, and I noticed two entries in tax_rates table. I deleted both and added new 20% tax rate for the existing tax class, and now everything works fine.