Can't change project backup location or render cache locatio

Want to set up new location and folder for both project backups and render cache. In Preferences, it implies you can set the project backup location. In fact, I haven't been able to change that.

In project settings, it implies you can change the file locations for render cache and for gallery stills. It allowed me to change the gallery stills location, but it fusses at me every time I create a new project,wanting to know if I really mean it.

However, no matter how I try, I cannot get it to let me change the render cache location. For some reason, it has decided that it wants it in my OS C: drive in a folder it created called "vol0". I have tried a dozen time or more to change the render cache location and save the project. Then,, when I open the project settings again, it's back to drive c:\vol0.

Very frustrating and surely must be a bug. If I'm doing something wrong, hope you can set me straight.

Thanks,
John