I can't see anything wrong with that, especially as intensive testing didn't seem to be one of the strongest parts of the Roundcube development so far.
And that compose_addressbook doesn't currently work with 0.9-master, is a pure fact. I'm just reporting this, but I don't blame anybody for it.
Thank you for reporting it. Im sure it'll be fixed at some point before 0.9 stable. Either by me or by an rc developer if it turns out to be an rc issue. I'll let you know.
Cor