Yes. The story is as follows: I was debugging BC 6.1.5 with a certain Polish server. We marked the test builds with letters - a, b, c, d... I caught wind of rumors of the DW20 pack featuring BuildCraft 6.1.x in it, so I contacted the developers with an unofficial build - 6.1.5l - knowing that 6.1.4 has some very serious bugs and it would be good if at least some of them were mitigated for the release. That's how 1.0.0 got 6.1.5l and 1.0.1 got 6.1.5n.
The next DW20 pack version should have the stable release.