from the exporter notes add in dec-2010
Adding bump map or specular map reduces the max number of decals you can have on each mesh.
The maximum number of decals you can have on a mesh without any effect layer is 7 (plus 1 for basic texture, for maximum limit of 8 texture layers).
Reflection takes 1 texture layer and subtracts 1 from the limit, reducing the maximum to 6 decal layers.
Adding Specular map also subtracts 1 from the limit.
Adding Bump map also subtracts 1 from the limit.
So a mesh with Reflection, Specular Map, and Bump Map has a maximum of 4 decal layers allowed.
so if you add only bump maps you add 5 decals or 6 decals whit no added maps like the older ones