Mac Mail Question

So using the native mail client that comes on every Mac I have Yahoo Gmail and my Hotmail accounts setup in it. Just recently my Yahoo account decided to create a new folder called "Bulk Mail" up until a few days ago it would always use the "Junk" folder but now it uses the "Bulk Mail' folder it created and I cant delete it or change anything. Gmail and Hotmail still use the Junk folder. Any thoughts on why this happened?