[Invalid] - update_attribute attempts to write accessor to the database

Let's say we have a class like this:

class Foo
  def bar=(value)
    # do something
  end

  def bar
    # return something
  end
end

Everything works great if I update attribute like this:

@foo.bar = 'something'
@foo.save

However, this:

@foo.update_attribute(:bar, 'something')

Blows up with:

ActiveRecord::StatementInvalid: Mysql::Error: Unknown column 'bar' in 'field list' ....

I can't for the life of me figure out why update_attribute tries to write that accessor to the database. Especially considering that internally it just assigns and saves. This is on 3.0.0.rc