With all due respect, how was I using the upgrade in the first place? If you consider that this is happening to players, it is because they already had the credits. There are no improved credits given with a spell the any player did not already have at the upgrade. Again, I suggest that when the magic upgrade is learned, then the comparable spell be removed from the trainer's list as well. This will help eliminate misunderstandings of what a player has or needs. This is not such an issue with the other trainers, BTW.
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When I dig alone -- I prefer to be by myself