setting attributes in Rails has_many :finder_sql relationship

Question

My question is somewhat complicated, but bear with me. My project has a number of models: User, Program, and Team. Users belong to multiple Programs. Programs have multiple teams, but Teams belong to one program. For each Program a User belongs to, he can belong to multiple Teams. (Think of this in an athletic context where users are athletes, programs are universities). So my models look something like this:

class User < ActiveRecord::Base
 has_many :user_programs
 has_many :programs, :through => :user_programs
 has_many :user_teams, :finder_sql => 'SELECT ut.* FROM user_teams AS ut
                                       JOIN user_programs AS up ON up.user_program_id = ut.user_program_id
                                       JOIN users AS u ON up.user_id = u.user_id
                                       WHERE u.user_id = #{id}'
 has_many :teams, :finder_sql => 'SELECT t.* FROM teams AS t
                                 JOIN user_teams AS ut ON ut.team_id = t.team_id
                                       JOIN user_programs AS up ON up.user_program_id = ut.user_program_id
                                       JOIN users AS u ON up.user_id = u.user_id
                                       WHERE u.user_id = #{id}'
end

class UserProgram < ActiveRecord::Base
 belongs_to :user
 belongs_to :program
 has_many :user_teams
 has_many :teams, :through => :user_teams
end

class Program < ActiveRecord::Base
 has_many :teams
 has_many :user_programs
 has_many :users, :through => :user_programs
end

class UserTeam < ActiveRecord::Base
 belongs_to :user_program
 belongs_to :team
end

class Team < ActiveRecord::Base
 belongs_to :program
 has_many :user_teams
 has_many :users, :finder_sql => 'SELECT u.* FROM users AS u
                                  JOIN user_programs AS up ON u.user_id = up.user_id
                                  JOIN user_teams AS ut ON up.user_program_id = ut.user_program_id
                                  JOIN teams as t ON ut.team_id = t.team_id
                                  WHERE t.team_id = #{id}'
 has_many :user_programs, :through => :user_teams
end

Now what I would like to do is be able to edit the users on a team from the Edit Team view using checkboxes, that is, include something like this in my edit form:

<% for user in @program_users %>
<div>
  <%= check_box_tag "team[user_ids][]", user.id, @team.users.include?(user) %>
  <%= user.name %>
</div>

<% end %>

And then in my TeamsController, do the standard :

def update
   # in case all users are deselected, create empty array as it won't exist
   params[:team][:user_ids] ||= []
   @team = Team.find(params[:id])
   if @team.update_attributes(params[:team])
     .......
end

When I try this however, Rails (not unsurprisingly) produces some pretty strange SQL:

When removing users 1237 and 1238 from team 1: Mysql::Error: Unknown column 'team_id' in 'where clause': UPDATE users SET team_id = NULL WHERE (team_id = 1 AND user_id IN (1237,1238))

When adding user 1242 to team 1: UPDATE users SET perishable_token = 'z7imelr6kqnwiD1dQtTt' WHERE user_id = 1242 (which is even more crazy... maybe something else is going on there...)

Clearly that approach is not going to work without some changes..... Note that everything worked fine when I didn't include any mention of program in UserTeam, and it was just a simple has_many :through join table for users and teams (I want to change the relationship so that when a user leaves a program and the UserProgram record is deleted, the MySQL foreign key constraints will cause the UserTeam records to be deleted as well).

What's the best way of editing these team members? Let me know if I'm completely off-base here. Thanks!