In fact its a feature of all modern Windows OS since XP SP3. You cant write into the Program Files folder without administrator rights. If you attempt, your files are redirected to ProgramData.

Windows does this for protecting its programs. The normal place for editing projects and files is your documents folder.

Although I recommend a separate partition or harddrive

A little fix for this:
The normal place for editing projects and files is a subfolder in your documents folder.