"Bad signature" when calling "check" in the edit-key menu: what happened to my public key?

[Michael Bienia]

Hello,

I see a strange situation when I try to edit my key:
1.) When I call "gpg2 --edit-key 0x968BD587" I see several lines of 
  "gpg: moving a key signature to the correct place"
2.) When I call then "check" in the edit-key menu, I get a line saying
  "218 signatures not checked due to errors" and many duplicate lines
  with a "[Bad signature]" at the end, e.g.:

sig%3        AAE3C5A0 2006-05-28  [Bad signature] 
sig%3        AAE3C5A0 2006-05-28  [Bad signature] 
sig%3        3E60B7DA 2007-03-11  [Bad signature] 
sig%3        3E60B7DA 2007-03-11  [Bad signature] 
sig%         C5D34D05 2007-02-25  [Bad signature] 
sig%         C5D34D05 2007-02-25  [Bad signature]

3.) After calling "clean" everything seems to be fine till the next key
  refresh when the errors comes back (and over 200 new signatures).

So it looks like the "error" already propagated to the key servers, but
doesn't seem to cause any harm (yet and as far as I can tell). But I
would like to know what happened to my key. Any ideas?

gpg2 is gpg (GnuPG) 2.0.8, the Debian package from unstable compiled on
Ubuntu hardy. But I see the same behaviour with gpg 1.4.6.

TIA,
Michael