There seems to be a problem with the agent if one tries to ssh-add a 2k DSA key.
Report on gnupg-devel from Michael Bienia:
$ ssh-add .ssh/id_dsa
Enter passphrase for .ssh/id_dsa:
Identity added: .ssh/id_dsa (.ssh/id_dsa)
But ssh-add -l didn't list it. Through further testing I found out it
was a problem with my ssh key:
$ ssh-keygen -l -f .ssh/id_dsa.pub
2048 [fingerprint] .ssh/id_dsa.pub