Here's an odd deal - I installed and enabled version 2.4 in my test 1.0-rc install. It works fine, except it seems to (somehow) interfere with displaying contacts in the Compose window. If I enable the plugin, selecting one of the addressbooks (either LDAP or SQL) in a compose window displays one or at most two contacts, and the status message of "Loading..." never goes away. Disabling the plugin reverts behavior to normal. No errors in the logs (even the ldap log) are seen.
No idea why it should interfere with the display of contacts in the Compose window, not sure what functions the plugin might leverage or share with the listing of contacts.