> The only reliable way of knowing if a given version of a xz decompressor can decompress a given file is by trial and error. The 'file' utility does not provide any help:

  $ file COPYING.*
  COPYING.lz: lzip compressed data, version: 1
  COPYING.xz: XZ compressed data

To me, this indicates a lack of data in the magic database used by file, more than something inherently bad with xz.