Preference de-sync between public & private keys

[mancha at mac.hush.com]

Hi. I recently encountered interesting (buggy?) behavior in the way gpg
deals with the preference order of key pairs.

If one sets a default preference order in gpg.conf like so:

default-preference-list SHA512 SHA384 SHA256 SHA224 AES256 AES CAST5 AES192 ZLIB
 BZIP2 ZIP Uncompressed

and generates a key-pair and exports each:

  $ gpg --export -a "temporary" > temp-pub.asc
  $ gpg --export-secret-key -a "temporary" > temp-pri.asc

the preference order coincides between public & private:

  $ gpg --list-packets temp-pub.asc
  [snip]
  pref-sym-algos: 9 7 3 8
  [snip]

  $ gpg --list-packets temp-pri.asc                                             
  [snip]                                                                        
  pref-sym-algos: 9 7 3 8
  [snip]

Now, if we change gpg.conf to have aes128 first in the cipher list:

default-preference-list SHA512 SHA384 SHA256 SHA224 AES CAST5 AES192 AES256 ZLIB
 BZIP2 ZIP Uncompressed

And change the prefs via --edit-key -> updpref/setpref, only the public key
gets changed. Private and public keys no longer coincide.

  $ gpg --list-packets temp-pub.asc
  [snip]
  pref-sym-algos: 7 3 8 9
  [snip]

  $ gpg --list-packets temp-pri.asc
  [snip]
  pref-sym-algos: 9 7 3 8
  [snip]

Thanks in advance for your time.