I have a feeling the mass inhibition is bugged. I have a Python and twice I've been inhibited by a much smaller ship, even when the NCP is the only ship on my radar. The first time it happend I'd lost my shields in a CZ and was fleeing, but a pursuing Taipan fighter (so really small in comparison) prevented me from jumping to SC. The second time I was in a debris field, I picked up a bounty for attacking a wanted NPC (that I'd scanned!) and once I'd dispatched the pirate I was attached and pursued by a single police viper, once more I was prevented from jumping to SC. The drive charges to about 30% and then simply stops.