The X, Y, Z and A "buttons"on the tool path page isn't buttons, only images. You can't zero the DRO's there. That you have to do on the main page or the MDI page. I don't remember the reason for doing it that way.
Anyway it's easy to change that if required.
If someone isn't familiar with Screen4 I can make a modified set file with active Zero buttons on the tool path page also.