Yes A6 does have problems with normal mapping on level blocks..the problems are:

1)Speed: any shaders applied to level blocks create a lot of slowdown.

2)Lighting quality: because the vertices of non-coplanar faces are welded, this creates bad lighting errors. This is because shaders interpolate data between adjacent vertices. There may some way to fix this, but I dont what it is, and anyway the speed issues make it pointless.

This is why level blocks are BAD for shaders, and why any modern egnine uses different kinds of geometry, where the user has more control over it.