From CTS 1.5 onwards there is a significant run-time terrain optimization that is on by default, and that gets around the hardcoded addpass issue with Unity terrain.
Background: every group of 4 textures adds a render pass to your terrain - with 16 textures this means that unity terrain renders in 4 passes - our optimization drops this to just one and removes many many draw calls.
The upside is that this makes a really significant performance improvement on terrains with more than 4 textures, but the downside is that if you are doing things like sampling the terrain textures to do footsteps then the data required to do this is now missing.
To get things back to what they were before go to the Optimization section in your profile and unclick "Strip Textures". This stops that particular optimization from running - and your textures will be left as is - so footsteps should be good again.