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other modpack releases, primarily Classic Reborn, and noticed IC2 release supplied with Tekkit Legends is rather outdated: IC2.Classic.Version.22.214.171.124. I then swapped IC2 126.96.36.199 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.
IC2 Miner stops mining. The mining pipe will not extend, and Miner will sit there consuming power by both the Diamond Drill and OV Scanner, but will not advance. Possibly related to Forestry blocks found in scanned area, but when manually getting Forestry blocks out of scan area, miner will not automatically resume. Have to restart mining by removing/reinserting Drill. Was reproduced in Tekkit Legends 1.0.10