I don't know about Yahoo Mail, but I am noticing that the internet today is doing odd things. Sites not opening when I have a great signal, refresh pages sending me to something unrelated. I thought I had a virus and opened my desktop machine. As I was being frustrated there, my significant other indicated he was having similar issues with his machine. We thought it was perhaps our ISP.
I'm happy to know this is happening to other people. I too have yahoo email and have had it happen several times in the last couple of weeks. I have also noticed that when I find an email in the spam folder that shouldn't be, I will open it, and the button "not spam" has been replaced with spam.