new version of gnupg signed with different key?

[privacy.at Anonymous Remailer]

gnupg-1.4.2.tar.bz2.sig was signed with key 0x57548DCD
but 
gnupg-1.4.2.1.tar.bz2.sig is signed with 0x1CE0C630, which is not in
turned signed with the old key.  Why?  How do we verify it's
trustworthy?

Thanks!