using Xml Disassembler to debatch orders

I have the following input document (it's a simplified version of actual data):

<Envelope>
<Order>
<Header>
<ID>1</ID>
<Amount>100</Amount>
</Header>
<Items>
<Item>
<ID>1</ID>
<Amount>100</Amount>
</Item>
<Item>
<ID>2</ID>
<Amount>100</Amount>
</Item>
</Items> </Order>
<Order>
<Header>
<ID>3</ID>
<Amount>100</Amount>
</Header>
<Items>
<Item>
<ID>3</ID>
<Amount>100</Amount>
</Item>
<Item>
<ID>4</ID>
<Amount>100</Amount>
</Item>
</Items> </Order>
</Envelope>

I want to use the Xml Disassembler Pipeline component to transform the above message into the following 2 messages:

Message 1:
<Order>

<Header>
<ID>1</ID>
<Amount>100</Amount>
</Header>
<Items>
<Item>
<ID>1</ID>
<Amount>100</Amount>
</Item>
<Item>
<ID>2</ID>
<Amount>100</Amount>
</Item>
</Items> </Order>

Message 2:
<Order>
<Header>
<ID>3</ID>
<Amount>100</Amount>
</Header>
<Items>
<Item>
<ID>3</ID>
<Amount>100</Amount>
</Item>
<Item>
<ID>4</ID>
<Amount>100</Amount>
</Item>
</Items> </Order>

But what i actually get is:

Message 1:
<Order>
<Header>
<ID>1</ID>
<Amount>100</Amount>
</Header>
<Items>
<Item>
<ID>1</ID>
<Amount>100</Amount>
</Item>
</Items> 
</Order>

Message 2:

Message 3:

<Order>
<Header>
<ID>3</ID>
<Amount>100</Amount>
</Header>
<Items>
<Item>
<ID>3</ID>
<Amount>100</Amount>
</Item>
</Items> 
</Order>

Message 4:

<Order>
<Header>
<ID>3</ID>
<Amount>100</Amount>
</Header>
<Items>
<Item>
<ID>4</ID>
<Amount>100</Amount>
</Item>
</Items> 
</Order>

That is, my problem is that the Xml Disassembler does not preserve the Items collection.

Am i trying to use the Xml Disassembler for something it cant handle?

In the message schema i have set the "Max Occurs" property to "unbounded" for the <Item> record.

I'm new to BizTalk, but the above seems pretty basic to me and i cannot understand why this happens.