Comment 3 for bug 1479110

IMO the interval setting would work both when the prohibit setting is unset or set to false. When you're using the interval settings, you aren't prohibiting negative balances, you're just telling the system when they can be applied. It therefore makes intuitive sense (to me) that the interval settings could be used in both instances.

Maybe we could change the label for the prohibit settings to say "Always Prohibit Negative Balances" to make it clearer for the user?