I just installed 1.0 on my Drupal 7 blog and noticed that all anonymous comments inherited the picture from the first commenter. Upon inspection, it seems that
_gravatar_load_account was at fault. When
user_load is called, Drupal returns the statically cached instance of the user object which, for anonymous, will always be the "first found". I guess this is linked to the Entity API somehow...
The fix I have applied is to pass the reset flag as TRUE if
$account->uid is zero... So the account loading line is now:
$account = user_load($account->uid, ($account->uid == 0));
I guess the alternative is to always overwrite with the "original" values if uid is 0?