> Your data is fine -- it's hidden while something else is mounted on top of the folder.

I thought that was the case. But the truth is I don't really understand how mount points work under the hood. Where is the mount point information actually stored? I'm guessing it's in kernel memory somewhere, but I don't really know, and Googling hasn't been much help. Is there an article somewhere that explains this?

> Rebooting will fix it.

Good to know.

> But you should be able to just unmount the filesystem

Yeah, you'd think. But everything I try to do to that directory results in "Input/output error".

> Does 'mount' list something mounted there?

Yes:

Python@fuse0 on /Users/ron/devel (fusefs, nodev, nosuid, synchronous, mounted by ron)

> Does 'df /path/to/folder/' reflect the FUSE filesystem rather than the underlying filesystem?

  [ron@mickey:~]$ df devel
  df: devel: Input/output error
  [ron@mickey:~]$ umount devel
  umount: devel: not currently mounted
  [ron@mickey:~]$ ls devel
  ls: devel: Input/output error

You can hopefully see why I'm puzzled. I would really like to understand why this is happening.