Re-download all newsgroup messages

[Dedalus]

I have configured a new newsgroup account and at the first connection,
when TB prompt me a dialog box, I have choice to download 30 headers
and then I have check option for mark all remain messages as read.

Now I have changed idea and I want to dowload all messages of
newsgroup. I have unscribed newsgroup, delete related account, deleted
News folder on ly profile and the recreate the newsgroup account and I
have subscribed the same newsgroup... but TB download always 30
messages.

ps: another question when I subscrive this newsgroup, I see various
duplicates messages (this happens after TB crash @
arena_malloc_small)... it is a know bug?