I've been seeing yahoo bots forcing 404s as well.
I haven't got the time to waste trying to get any info/response from yahoo. I've pursued mail server problems on two occasions and each time got nowhere. The replies I DID get were pretty much standard boilerplate and my subsequent attempts to get more info/action were not replied to.
I'm used to yahoo's bad behaviour on mail and web servers (very frequent hits on bot IPs with no bot UA, for example).
Basically, if it's a yahoo bot UA on a yahoo bot IP (ie not just any old yahoo IP) then just reject it and don't worry.