Hi YeaBuddy.
So far that I know, C root is protected by the system. It is actually good to keep the root is clean and clear from unnecessary files being dumped to it. But, you can actually save your work to C root by running the program as a real administrator (right click the program, and choose run as administrator and you are prompted as usual). But you have to take a note that your files will be saved as read only files. It means if next time you open the files you will see it opened as [read only], unless you open it by the same way (as administrator, and again you are prompted to open it as read only, or not).
But, if you really need to have some file saved to drive C, then create a folder in it.
I have no further explanation why it happened to your other drive.