I have been working with the Pidgin dudes on this issue: http://developer.pidgin.im/ticket/4269
The problem is that Pidgin is not enabling XHTML support for auto-joined chatrooms joined at login. Debuging the interaction, it was discovered that Openfire is ignoring this request:
<iq type='get' id='purple846aa516' email@example.com'><query xmlns='http://jabber.org/protocol/disco#info' node='http://jabber.org/protocol/muc#traffic'></query></iq>
see debug2.log on the pidgin ticket.
Any thoughts on this?