Probably someone who's related to to a staff member on the show.
The BBC does some of the worst leaking "officially".
Joe's death was spectacularly crap. In a matter of days everyone had forgotten about it, and Bert was not remotely bothered.
It does kind of suggest the writers don't care about the characters, the way the exits are done.
Johnny Allen dying of a heart attack, Pauline keeling over (and no Julia's theme!), Ruby's argument with Stacey being cut out, Joe killing himself then everyone forgetting about it.