the way it looks like it works is anything you put on the stack after a split second card doesn't get cast. Anything that goes on the stack before the split second card does. If you had two split second cards on the stack, neither would get cast.
All the cards go on the stack simultaneously, but you get to choose the order.
You are wrong, and clearly don't have a very good grasp of Magic terminology. Please don't try to explain things you don't understand. CASTING a spell means taking it from the zone it's in, adding it to the stack, and paying it's costs as needed. You never CAST a spell that's already on the stack. For spells arleady on the stack, the action where it takes effect then goes into the graveyard is called RESOLVING.
Now that the terminology has been ironed out... If you somehow achieve the gamestate where a Spell X with split-second is on the stack, and Spell Y is above it, assuming priority is passed, the stack will clear without incident. Split-second does not stop things from resolving, it only prevents new things from being added in the conventional way. In the scenario above, Spell Y will resolve, then Spell X will resolve. If that same gamestate was achieved and Spell Y also had split-second, the same thing would happen. Spell Y resolves, then Spell X resolves.
I have to wonder what you thought would happen if the rules worked your way. Is the game a draw if you get a spell onto the stack above one with split-second? Neither player can cast spells or activate abilities? Forever? The turn won't progress since the stack never clears, so it's not like you can attack someone to death either. Also, why doesn't split-second prevent the spell which contains the ability from resolving?
Apologies to all for reviving a relatively dead thread, I've been travelling for the last few weeks. I was intending to just catch up on what I'd missed but this was too blatantly wrong for me to leave uncorrected. God help any poor bastard who read this and actually believed that was how the mechanic worked.
