imapsync & proxy user

[Adam Tauno Williams]

imapsync-1.188 cyrus-imapd-2.2.12-27

This works:
./imapsync \
  --host1 scratch --user1 adam \
  --authmech1 PLAIN --password1 ******* --ssl1 \
  --host2 sardine --user2 adam  \
  --authmech2 LOGIN --password2 ****** --ssl2

But I can't get the proxy user to work:
./imapsync  \
  --host1 scratch --user1 steve --authuser1 adam  \
  --authmech1 PLAIN --password1 ***** --ssl1 \
  --host2 sardine --user2 steve --authuser2 adam  \
  --authmech2 LOGIN --password2 ***** --ssl2

I need to sync a whole bunch of user's accounts.

With the second example it fails with: "Error login : [scratch] with
user [steve] : 1 NO Login failed: authentication failure"

I have - 
proxyservers: cyrus adam
admins: cyrus adam
- in imapd.conf on both sides.

I also tried "proxy_authname: adam" which I saw in a post, although it
doesn't seem to relate.