Update: a new public beta of Messenger Plus! is available now:
msgpluslive.net/news/2009/01/11/another-year-another-version/
The current release of Windows Live Messenger and the public beta of Messenger Plus! Live are not 100% compatible. While some features do work not all. This was expected to happen as things can change when a product (Windows Live Messenger) goes from beta to release candidate.
Patchou is aware of the incompatibility and when we know something you will know something.
The current version is:
Image courtesy of Neowin.net