Just a quick poke here since I don't want to reopen the issue on GitHub, but could you put a 1.0.3 up on Curse with the EntityMinecart.getCartItem() fix?
Also, a huge, huge thank you for making this mod, it's pretty much central to distributing stuff long-distance on my server! Three diamond chest carts in a train makes for a LOT of stuff moved at once (As well as looking awesome!)
Sure! I was going to post it yesterday but ended up forgetting (sorry!) I'll upload it now, it should be up in a few minutes
Edit: It's been uploaded! Let me know if you run into any other issues