Exporting a material with multiple diffuse textures in COLLADA format

Question

I need a Blender export format that handles materials with multiple diffuse textures in it. Specifically, I want to export a mesh with a single material and two diffuse textures and a single stencil map. The blender COLLADA exporter appears to ignore two out of the three textures in my material. All three are referenced in the export file as:

<library_images>
   <image id="Grass_1_png" name="Grass_1_png">
     <init_from>Grass_1.png</init_from>
   </image>
   <image id="stencilmap" name="stencilmap">
     <init_from>stencilmap.png</init_from>
   </image>
   <image id="BlueMarbleSlabs_png" name="BlueMarbleSlabs_png">
     <init_from>BlueMarbleSlabs.png</init_from>
   </image>
</library_images>

However the library effect diffuse component only references the last texture in the material texture stack:

<diffuse>
    <texture texture="BlueMarbleSlabs_png-sampler" texcoord="UVMap"/>
</diffuse>

Does anyone know if this is a limitation of the COLLADA exporter? If this is the case then I'll need to modify the Assimp COLLADA loader for my purposes. Thanks in advance.