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Detail:
  LanManFS does not like it if you create (independently, using a PC or
    otherwise) files with names like "myfile,fff" which you intend to
    be displayed as files with type &FFF (ie. Text) on a RISC OS machine.
    If you tried to access the file for reading it, such as loading it
    into an editor, that worked due to the name matching resolution.
    However, any attempt to update the file caused LanManFS to attempt
    to write the file without the extension and not notice that a file
    with a ,fff extension already existed (Text files are special cased
    in the current implementation of name translation - see LanManFS
    Functional Specification for details and rationale).  Attempts to
    save typically succeed (giving you two files: myfile and myfile,fff)
    but generate "Operation not permitted" or such like.  This stemmed
    from the attempt being made by LanManFS to rename a fil...