If anyone has encountered this bug and successfully modified the code generated by the VSPackage project template to fix it, please post the fix.
Steps to reproduce
1. Create new project > Extensibility > Visual Studio Package
2. Run through wizard and select Custom Editor
3. Run in Debug mode
4. From Experimental Instance, create a new project (e.g. c# winforms), or just open an existing one
5. File > New > File > create new instance of custom editor
6. Save the file in the project folder and add it to the project in solution explorer
7. CLOSE THE CUSTOM EDITOR designer if it's open (e.g. MyExtFile1.vspackage1)
8. Reopen it
9. WHILE OPEN, RENAME THE FILE in solution explorer (e.g. change to XXX.vspackage1)
10. Type some text
11. Save the file
12. Close it and reopen it.
13. Text is not there. If you look in the project folder, you will see it saved the file using the old file name (MyExtFile1.vspackage1)
