I tried searching the web for that message but you seem to be the only
one getting it in this circumstance. :)  Alas.
If you can still reproduce it occasionally with some kernel, please
report the symptoms to linux-acpi@vger.kernel.org, cc-ing either me or
this bug log so we can track it.  Be sure to mention:
  - precise steps to reproduce, expected result, actual result, and
    how the difference indicates a bug (should be simple enough)
  - how reproducible it is
  - which kernels you have tested and what happened with each
  - full "dmesg" output from booting an affected kernel, as an
    attachment or link
  - acpidump output, as an attachment or link
  - any other weird symptoms or workarounds
Hopefully someone there can suggest a way to figure out what is
happening, for example by applying some patch or enabling some
debugging feature to be ready for when it happens next.
Thanks again for a clear report, and sorry I have no better advice.