I believe I've found a bug with the grinder:
If you run out of EU in your storage while it's running, it'll reset, and if you aren't producing enough EU to keep up with it, it'll just keep eating what you produce and then resetting when it runs out. This isn't really a big problem but it's inconsistent with all other machines. The actual bug part, however, is that I removed the wire, let my MFE charge to about 60k EU, then placed the wire back. The grinder now gets to about 80% done processing the ore, then resets back to 0% even though there's plenty of power. It just keeps doing it until it drains the MFE.
Breaking the machine and replacing it didn't fix it.