My guess would be that there is still some sort of short. I think you were right to suspect something stuck down in the jack, but it sounds like something inside the casing may be shorting on the terminals. Since you said it opened up the voice command thing, I would suspect that the 4th pole was triggered (or whichever the microphone button would be for a 4-pole headset). As far as I know, the microphone/media button is activated when the jack senses a short on a specific pole. But, it would have to think that you have inserted a 4-pole plug. I don't know for sure, but I assume it does this by checking opposite sides along the plug shaft to see how many distinct conductors are present. If it thought your typical 3-pole plug was a 4-pole, there would probably be another "conductor" present, i.e. the trouble-making short-circuit.
Unfortunately, it sounds to me that you have a hardware problem. If you were adventurous, you could open up the case and inspect for the short. It may be something simple lying across some solder joints or something. However, it is probably safer to simply get the warranty exchanged refurb. I have one myself since my original one had this obnoxious echo that the caller on the other end would complain about. The refurb unit works great!
It's a bummer, but I doubt you'll even know the replacement is a "refurb". Sorry I don't have better news or advice. Good luck!