I still have a problem with this CS response. Not only is this not the manner I recall seble explaining the system during the beta process, but it also seems to run counterintuitive to the process things seem to go through when changing minutes promises..
Consider -- if CS is correct, the whole deal of upgrading a minutes promise from 15 to 20 wouldn't require any complex sequence of undoing and redoing. Just add the extra boost for the 5 extra minutes, done. Also, there'd be no need to add a penalty for canceling stuff out because it would be a simple product of dropping the credit from that action, etc.
Of course, seble could answer this really easily, but since he hasn't shown on the forums since the game was bought, I have as much opportunity to get the answer from the Almighty himself in the Second Coming.