I had Behemoth_miner engines drop, however, I cannot unload them at a station.

This is not a bug, at least, not the undroppable part. Lately many "engines" have been popping up in convoys. Long ago, these used to be equippable on different ships. They were removed from the system, and the items removed.

The bug here is that the engines appeared at all.

I can just hear all the laughing behind the curtains.