`tested-with' in package

[Serge D. Mechveliani]

Who knows, please, what is the matter with the  `tested-with'
field in a package specification in  ghc-6.4 ?
Among the attempts 

  tested-with:  ghc-6.4, 5.02
  tested-with:  ghc-6.4
  tested-with:  GHC-6.4
  tested-with:  "GHC-6.4"
  tested-with:  ghc
  tested-with:  GHC

only the last one satisfies the `configure' command
                                      runghc Setup.hs configire --ghc
Other variants yield
" Line 12: Parse of field 'tested-with' failed.
"

Thank you in advance for explanation.

-----------------
Serge Mechveliani
mechvel at botik.ru