Ditto might be unobtainable as of yet, but transforming Pokémon have found their way into Pokémon Go. Reddit users have reported Pokémon showing up as one species and becoming another when caught, such as one user showing their Bulbasaur had transformed into a Caterpie.
The glitch is unpredictable at the moment with a user reporting their Pidgey becoming a Nidoran while another found a Shellder that became a Spearow. A telltale sign for some players has been an unusual CP number, with one Imgur user showing screenshots of a Caterpie CP 1212 (i.e. impossibly high for that Pokémon) turning into a Charizard after being caught.
Some user have speculated this may be related to the recent nest changes. The common consensus is the issue is with the Pokémon Go servers and not the client, meaning it’s likely Niantic can resolve this issue without the need for an update.