1. Close all files and projects
2. Open C file
3. Edit C source, don't save.
4. Project Compile, complete project process, file does not save.
5. Close the project, the C file remains open.
6. Close C file, reopen project, open C file from project manager, now auto save works.
The IDE does not consider the file part of a project created in that fashion until it is loaded from the project manager.