Cannot ignore elements inside structure

I need to ignore elements inside XML, which I do not want to map. According to manual, this is done using <structure> element without field. This works unless structure is inside structure (see comments):

<binding name="BAST" direction="input">
<mapping name="METADATA" class="hr.siemens.m2y.streaming.model.PlayList" value-style="element">
<!-- works -->
<structure name="version"/>

<collection field="media" factory="hr.siemens.m2y.streaming.model.PlayList.mediaListFactory">
<structure name="product" type="hr.siemens.m2y.streaming.model.Media">
<value name="ean_code" field="eanCode"/>
<!-- FAILS -->
<structure name="bast_product_id" usage="optional"/>

Binding compiler reports:

[bind] Error: No compatible mapping defined for type hr.siemens.m2y.streaming.model.Media; on structure element at (line 14, col 59, in bastBinding.xml)