Category: Animation system
2.46 was the first version to ever include pyconstraints and always worked for me. In 2.47 they work in Blender's 3D view, but are ignored at rendering time, or simply do not work at all.
Attached image 1: Image showing how it did work under 2.46
Attached image 2: Blender 2.47
Attached file contains armature from my example. The constrained bones copy the Y axis of their targets but not X or Z rotations.
Load in 2.46 (only 2.46), everything works fine. Load in 2.47, all bones which should be constrained are in their rest positions. The console reports no errors.