When playing as a minor league manager in a historical league, there are often cases where I get emails detailing a particular transaction that does not actually occur.
Here is an example. Here is the mail I received about player transactions:
And here is the roster I see after receiving that mail (there were no other player transaction mails received):
Note that Rezzori is not on my roster, and that I did not actually lose Ruiz.
I've seen this error at least as far back as OOTP11.