I saw that too. I don't know what "improvements" were made, but I did find that in the Discover Card site and in the Key Bank site (where I have accounts), I could not redeem my cashback bonuses for my credit cards. Both sites have been updated recently by the respective businesses, so I don't know if Safari is to blame or if Discover and Key techs didn't do their homework. I was able to redeem those bonuses in Firefox.
I will be contacting Discover and Key tech support for comment.