Go Calc 1.5.1 has been submitted to the App Store.
In Go Calc 1.5.0 (don't try this!) you can move a category into itself. This category will then no longer be accessible from Go Calc. This update stops the user from doing this (by not displaying the category's category in the category chooser). It will also move any 'lost' categories back to the home category.
This update should be available within the next 7-10 days.
Apps On The Move