You may want to catch up on recent BuildCraft changes that have been compiled
here while we wait for an official changelog (considering BuildCraft remains in prerelease status and hasn't been in a "release" status since 3.1.5 for Minecraft 1.2.5). There's been some considerable tweaking done on top of all the porting required for SMP, and the changes continue as you can see in some of the replies. =)