MinecraftForge/MinecraftForge — pull request #1050 by CovertJaguar (2014-04-29 21:09:06+00:00)
Title: Flexible Rail return value was inverted between 1.6 and 1.7

Between 1.6 and 1.7 the return value to BlockRailBase.isFlexibleRail()
was inverted. While this is not a huge deal and could be worked around
by simply inverting your return value, it does mean its no longer
consistent with the function name and javadocs.