In XNA 3.1 is there any other way to disable depth in 3D Worlds using DirectX models other than

GraphicsDevice.RenderState.DepthBufferEnable = false;

?

The reason for my question is I have quite a huge program which offers a 3D World with a couple of 3D DirectX models inside. Depth was never an issue since it ever worked fine but since a few days after doing some modifications my models are all depth-translucent i.e. depth-buffering and/or culling seems to be disabled.

But in my whole source code I never touch any of the options related to Depth or Culling which means I never turn these settings on explicitly nor turn it off somewhere.

So I am searching for some other statement maybe related to the GraphicsDevice that implicitly turns depth off - but I can't find it.

(Sorry that I don't post any source code but I have too much source code and I simply don't know where to search)

UPDATE:

These are a couple of simple objects seen with correct depth.

These are the same objects in their current state.