If I were in your position, I'd go back to the shop where you bought it and explain what happened. Ask for a replacement, this seems like a shortcoming in the production of your Minibrute, especially when in your manual no warning was given about storing conditions and a possible effect on the paint. And if you do get a replacement, you'll have to make sure the same won't happen again by covering the lettering with sticky tape, for instance.
Of course the paint decay shouldn't occur in the first place. But nevertheless, it seems that there are certain conditions in your studio that are the cause of the decay. Conditions one can only speculate about. Does climate control also regulate the level of humidity? If it can't relate to temperatures, then maybe it's due to that?
In the possible situation of a replacement, maybe it's best to not take that Minibrute to the studio and wait if it's going to show the same symptoms within a month, in a different place. If not, you'll know for sure there's a studio issue. But if the paint wears off again, if only in the slightest bit: cover it off with tape!
Let's hope the staff at the store where you bought it will be cooperative! They should care, because they want to know if this could happen to other sold Minibrutes as well. Good luck.