ActiveRecord in Rails 2.1.0 misbehaving for Aggregate Attr.

I am not sure if this is a bug in ActiveRecord or is this the intended
behavior. If it is then it does not make sense to me.

In a nutshell: If you change an aggregate object attribute created via
composed_of method (see Agile Web Development - Second Edition Chapter
17 page 313 onwards) and then save the model, the change to the model
(composite attribute specifically) will not be saved UNLESS you
explicitly set the partial_updates attribute for that model to false.
Specific use-case:

I have an Account model that shadows the accounts table in database.
This account object contains a composite object (amongst others) called
BillingAddress defined within the Account model class as follows:

  composed_of :billing_address,
    :mapping => [%w(address_1 address_1), %w(address_2 address_2),
%w(address_3 address_3),
                 %w(city city), %w(state state), %w(zip zip),
%w(card_country country)] do |params|

To test this theory, in the Rails Console, I "found" and existing
Account object in the database using

acct = Account.find(id) -- where id is a specific account id

Now I create a billing address object:

ba ="123 Lane", nil, nil, "City", "State", "12345",

Next, I assigned the newly created billing object to the account
object's billing_address composite attribute as follows:

acct.billing_address = ba

Now if I save this as:

Then no update statement is triggered as it does in Rails 2.0.2.

If however, I set the partial_updates for the Account class to false
BEFORE assigning the ba value to acct.billing_address then the update
statement is triggered. That is:

Account.partial_updates = false
acct.billing_address = ba

This will trigger the update which is what I want.

Note that partial_updates works as stated for simple attribute updates.
That is:

Account.partial_updates = true
acct.address_1 = 'xyz street'

correctly triggers the partial update where only the address_1 attribute
is updated in the database.

Has anyone else experienced a similar problem with composite attributes?