Pokewalker IVs confusion.
Just a coincidence, besides, those characteristics don't guarantee a perfect IV, just that the highest IV will be of that stat and will end in a 6 or a 1.
If you demand 'proof' I can trade to you several group C pikachus with absolutely horrid IVs upon your convenience.
Most apt suggestion, further expounded upon.
Or, you can just skip Stantler if it's too much bother and teach thief to something that will OHKO it every time, though you'll get a lot of oval stones. Also, chaining them is generally a good idea, Chansey isn't very common.
It's your DS, not your game. I've had the same issue with my DS, and several of my friends have as well. Best thing to do is to simply try and remember to save as much as possible and turn off your DS when you're finished with it. (I'm going to assume you have a DS lite? It has never happened to me on my DSi or my old DS classic, just on my DS lite.)
If the Everstone was not placed on the ditto or on the female the Everstone would have failed. If your parents were from different countries it would also fail.
Now, for your other question, if you have one power item on you have a 100% chance of passing down an IV, this is not affected by having the female hold an Everstone (Note: I am very happy with that set-up. Yay Gamefreak.) If both parents hold power items it seems to be around a 75-80% chance that any IV will be inherited (Two parents with perfect IVs in attack and speed respectively holding Power Anklet and Bracer, corresponding to their perfect IV gave me 79 eggs with a perfect attack IV, 76 with a perfect speed IV, and 6 with neither a perfect attack or speed IV out of 100 eggs generated.) Make of that what you will.
In Heart Gold and Soul Silver, yes. As do Shaymin and Deoxys' seperate forms. I'm not entirely sure about Platinum.