Right clicking a clone of a command block (Cloned with /clone) sometimes causes the game to crash. However, if since the last clone, the player relogs, the game does not crash, and shows the correct command in the command block.

StackTrace:
java.lang.ClassCastException: apl cannot be cast to apj
at akd.a(SourceFile:62)
at bmj.a(SourceFile:268)
at bbm.aj(SourceFile:1219)
at bbm.p(SourceFile:1555)
at bbm.ah(SourceFile:764)
at bbm.f(SourceFile:718)
at net.minecraft.client.main.Main.main(SourceFile:154)