Scratch disks are set on a project per project basis.
For each Project, you have the option now on where to assign all of the Scratch Disks. That can be altered by Project, as is required.
Good luck, and hope that this helps,
This is really a feature request. This is one of those changes that adobe has made to premiere that may or may not have been a good decision.
The only workaround you have is to make a default project setup with your proper paths and then every time you want to start a new project you load it in and save it wherever you want with the proper name and your set..
It would be easy enough for them to fix, save the paths in the project file but allow you to set the default path to be something other then "same as project"
Set up a template project and always start with that.
Moving this to project level was DEFINITELY a good move. Now we don't have to switch the damn setting every time we switch projects being worked on.