Here is the reply from Altium:

In the absence of any mechanical layers or prior default usersettings, if I add a STEP model, it goes to Mechanical 1. However, 3D bodiesfrom our content library team uses layer Mechanical 13.

This may be the cause ofthe confusion. At the end of the day, the user needs to decide which is betterfor their assembly drawings, but from a 3D model standpoint it almost doesn'tmatter which layer is used.

If you download a Footprint with 3D Model from the Altium library vault, the 3D STEP is on layer Mechanical 13.

We're only defaulting to what the Altium Vault defaults too.

But in V2015.02 you'll be able to change the layer assignments.

Well, then we'll have to fix that so you can edit the layer assignment in V2015.02. We'll have a .02 pre-release tomorrow here - www.pcblibraries.com/downloads (actually there already is a .02 pre-release there right now that fixed an Altium through-hole script bug).

But that leads us back to the "default" 3D STEP layer anyway. We get our information from a large pool of users that say that the "default" 3D STEP layer is Mechanical 13.

We'll change the default layer assignment to Mechanical 1 if Altium corporate agrees with you. I'm waiting for their reply answer right now.

You can change any of the layer assignments in the CAD tool export GUI.

Just select "Save Entries as Preferences" after you edit the layer mapping.