I further looked into this, and compared IC2 MOD JAR against other modpack releases, primarily Classic Reborn, and noticed IC2 release supplied with Tekkit Legends is rather outdated: IC2.Classic.Version.1.1.2.1. I then swapped IC2 1.1.2.1 jar with industrialcraft-2-2.2.793-experimental, and tested Miner in Creative mode. Miner now mines Forestry blocks, and no issues detected thus far. Hopefully this will help anyone else running into same behavior.
