PC Laptop & Firefox: When setting practice minutes it allows you to set any attribute to negative minutes, then adds the total of those negative minutes towards the usable (or leftover) minutes and can be applied elsewhere.
However, when you click the "Save" button it freaks out and redirects to an error page, which says "SERVER ERROR in '/WhatIfSports/hd' Application" then "Value was either too large or too small for a unsigned byte." Here is a screenshot.