To be perfectly honest, I pushed for an explanation but haven't been given an in depth answer. Basically, I've reported it to them and they've left it with the engineering team who were able to work out the problem. Unless it has affected a multitude of users the information I get back is limited.
Unfortunately this is exactly what I've said.
This is the reason they SHOULD feedback the solution, in case it happens to users in the future.
It is plainly ridiculous that they haven't said anything, as it puts the moderators in a position to have to go back and ask the Yahoo folk to investigate all over again for a future fault of the same nature, rather than saying "Here's one we cleared earlier and how".
This costs time, effort and end user anguish which could all be avoided.
The webchat that I had prior to posting here was next to useless. The guy dealing with me - and his supervisor - obsessed with this being an apple issue, and kept asking me to close the webchat even though they had not provided me with a way forward. I self-diagnosed the 'rogue email' issue, and yet they were still convinced it was an Apple issue. I think they need to "fix" that too...