This got me too. It seems that the ordering has been changed so that it:
1) Looks for a folder called silverstripe-cache-path-to-web-root in the web root
2) Looks for a folder called silverstripe-cache-path-to-web-root in the system tmp folder and if it's not there then it tries to create it
3) Falls back to a folder called silverstripe-cache in the web root if 2) fails (which is unlikely)
Whilst I can see the point of having a site unique cache directory if you create it in the system tmp directory, I can't see why it needs to include the path in the folder name in 1) - seems kind of redundant.
Creating a silverstripe-cache subfolder in the main Sstripe folder is working
and there is no more /tmp/silverstripe-cache-something folder. I think this
subfolder should be already created in the default install SStripe package with
acces rights verification like some other folders.
EDITED : and a .htaccess to forbid direct web acess of files in that folder :)