Notepad won't open the file (but other text editors will)

[Dwedit]

Working on a file system (read only). I seem to have directory traversal and reading files working fine, but some programs are having compatibility issues.

When I try to open a file with Notepad on my filesystem, it displays "Make sure a disk in the drive you specified", and fails to open the file. Other text editors work fine, it's just Notepad that doesn't like it.
Opening a file under Notepad works fine in the Mirror filesystem.

I'm also getting error messages when I try to launch an EXE file on my filesystem under the x32dbg debugger. I either get ERROR_PATH_NOT_FOUND, or ERROR_PWD_TOO_SHORT (a nonsensical error message about a password being too short)
Debugging an exe does NOT work on the Mirror filesystem either, I see the same error messages.

Does anyone have any idea what could cause Notepad to think a disk is not inserted?

[Dwedit]

I am seeing this sequence of calls: Cleanup, ReadFile, CloseFile

Is Cleanup getting called prematurely?

On my FS, ReadFile was failing because it happened after Cleanup.

As for the "Debugger" issue, it appears that registering with mount manager on mount fixes x32dbg. x32dbg was trying to canonicalize the path by using something like GetFinalPathNameByHandleW, and that requires using the mount manager.