To avoid BeerSmith getting "confused" about volumes and calculations, make sure that your recipes are all closed when you make changes to the units or advanced options. I'm not saying this happened, just that it's a good practice. BeerSmith seems to make some calcs when you open the recipe and not when the units are changed.
Second, you can create a default recipe that has all of the measured fields zeroed out, as well as starts with all the tedious things (like irish moss) that go into every recipe.
Just create the recipe with your equipment, some basic pale malt and foundation bittering from your favorite hop. Add your favorite yeast, some irish moss and then your favorite mash, fermentation and carbonation profiles.
Click the "Save as Default" button, hidden in plain sight right next to the "Remove Inv" icon. Confirm and there ya go! When you click "Add Recipe" it's ready to modify.