usage="optional" not working for a particualar structure element in binding XML

Hello,

I am getting a typical error. I have a master binding XML which included a child binding XML within which a binding definition is like

<structure map-as="ns82:tsetItem" get-method="getTsetItem" set-method="setTsetItem" usage="optional" name="tsetItem"/>
<structure map-as="ns111:testEvent" get-method="getTestEvent" set-method="setTestEvent" usage="optional" name="testEvent"/>
<structure map-as="ns13:Characteristics" get-method="getCharacteristicList" set-method="setCharacteristicList" usage="optional" name="CharacteristicList"/>

Like this there are numorous structures defined. But the for 'tsetItem' surprisingly the optional is not working. When i post XML, and I am not passing the 'tsetItem' the marshalling fails and says 'missing required object'. The 'tsetItem' structure is made up of a number of other types which is defined in another binding file.

I have no clue how to fix this, but the appllication payload must pass this request while the 'tsetItem' does not appear in request XML.
Please can i get a help here. This is very critical for me.