Draw call count not consistent in prefab vs model

I have a model of a light pole (2 materials, 9 meshes).

Some time ago, I made it into a prefab and attached some physics and scripts to it. Today I noticed that my draw calls for these electric poles weren't being batched.

First, I removed all the components from the prefab -- still not batching.

Next, I put just the model into the scene (without a prefab) -- it was batching. This is the same exact model referenced from my prefab, yet now it's batching.

These poles aren't referenced in any scripts. There are no lights in the scene.

So finally, I created an empty scene with my prefab light poles. This time, everything was batching properly, including my prefab. Does anyone know why this is happening?

I'm not sure why it would instance in one case, and not in the other. Some things to consider:

Unity will only batch prefabs of ~300 verts or less.

Unity appears to have trouble batching prefabs with 2 or more materials.

Unity will not batch skinned meshes.

Check out this thread for help with reducing draw calls: http://www.unifycommunity.com/wiki/index.php?title=MeshMerger