No, it isn't that, thanks for that info anyway.

The map compiler requires a visible block before it will build a map entity. I have noticed this is no longer a requirement to build a level, so perhaps it was an oversight?

Sometimes it is useful to bundle some meshes together in a map entity, and with a model level there is no reason to include a visible block (currently I am hiding a tiny block inside a model to get around it, but that isn't very elegant).

This is with the current BETA and the current release versions.