Thanks for the help, William! It worked. Eventually.
I had changed both paths, for apps and files to D:\, but CC still installed on the C:\ drive.
Thought I'd give it a second try, though, since it worked for you. Uninstalled, downloaded the CC manager and saved it on my D:\. Changed paths to D:\Adobe and tried installing Photoshop and it installed in the same folder as the manager (D:\Downloads). So, the correct drive, but the wrong folder.
This gave me an idea. Uninstalled everything again, downloaded the manager to D:\Adobe and Heureka! Photoshop is now installed there too. Let's hope the other programmes/apps will do the same.
But I have to say I've never experienced anything like this with any other software. Changing the installation path really is a basic feature... And I have yet to find out which scratch disk Photoshop will be using.