I don't know if this is a bug or if this is now how things will be - but I could not find anything in the release notes saying this had been changed:
Previously before this new season, all the duty officers in the academy Duty Officer Stores (I assume both factions - I only tested in federation side) only gave out ONE of each duty officer (for dilithium) available there. You could not have more than one duty officer from the store that had the same name (it popped up a message on screen saying you could not buy more than 1 of the same) - but now it seems you can buy multiples of the same. Or at least - I was able to buy one I had definitly already bought there previously.
This must be a good thing - we can buy as many duplicate doffs from the store as we want!
But I somewhat doubt this was intentional (or at least this is what I think - hope you don't think i'm being nit-picky or something - lol ). I mean (provided you have enough dilithium of course) allowing the exact same duty officer with the exact same traits etc to be bought over and over again somewhat eliminates the point for different trait doffs - just saying.
But anyway, if this isn't a bug and the store has been changed to allow multiple identical doffs to be bought, they should probably make a note of it somewhere I reckon.
In the mean time, bug or no bug, looks like we all got extra duplicate doffs we can buy - yay!