The orientation of a prim is affecting its bump-map shadow effect (relief). An upside down prim seemingly inverts the effect, turning an emboss into an engrave. This is showing in Firestorm and LL viewer, which was updated moments ago.
The effect is shown in the images below
-First is a single prim 1m square
-Second section is a 4x4 grid of 0.25m prims, rotated differently but textures aligned
-Third and Fourth are the same things using Materials rather than Blinn-Phong, which do not have the issue
The bug is the Second section showing differing relief amounts even though they are co-planar and same orientation. The difference here is the orientation of the prims themselves.