Rails - Dec 2005 - More HABTM Save Problems/Issues.. bugs?

I seem to be having a problem working with an object which has a  
HABTM relationship with another object I know there''s been a lot of  
talk recently about problems using dual HABTM in a single object but  
I believe this may be a separate issue. It appears like I''m unable to  
persist this relationship (i.e. the object saves but none of the  
entries in the join table are created even though the "arts" object  
is populated) during the initial save, yet it I update the exact same  
object it properly updates the database. I have an model which looks  
like the following:

	class Event < ActiveRecord::Base
		...
		has_and_belongs_to_many :arts
		...
	end

for testing purposes I have a form with some fields that I''m using to  
populate this object:
	<input type="hidden" name="event[art_ids][]"
value="1">
	<input type="hidden" name="event[art_ids][]"
value="2">
	<input type="hidden" name="event[art_ids][]"
value="3">

finally my controller, when I attempt to save the object it doesn''t  
save the 3 join rows in the arts_events table (even though they do  
exist in the object), my save method looks like:

	def add
		@event = Event.new( params[:event] )
		@event.user  = @session[:user]

		if @request.post? and @event.save
			redirect_to :action=>:view, :id=>@event.id
		end
	end

the odd thing is, is when I access the EXACT same form but update  
this object with the following update method it creates the 3  
arts_events
	
	def edit
		@event = Event.find_by_user_and_id( @session[:user], params[:id] )
		@event.update_attributes( params[:event] )
       		
		if @request.post? and @event.save
			flash.now[:notice] = "event record has been sucessfully updated"
		end
	end

now to further prove my point that it doesn''t work with saving, but  
it does work with updating I change the add method to the following  
which saves all the 3 rows in the arts_events table

	def add
		@event = Event.new( params[:event] )
		@event.user  = @session[:user]

		if @request.post? and @event.save
			@event.reload
			@event.update_attributes( params[:event] )
			@event.save
			redirect_to :action=>:view, :id=>@event.id
		end
	end

Any insight anyone could provide would be appreciated.. Thanks

Chris