Spiky-Eared Pichu Trouble

About a week ago I used a Pikachu colored Pichu (downloaded PKM file into my savegame) to unlock the Spiky-Eared Pikachu event. All went well and I dumped the Pichus in my box.Now it's a week later, I checked my box, the Spiky-Eared Pichu has changed into a normal Pichu. The moveset is still the same, stats are still the same, meeting place, level, all still the same, except it's not Spikey-Eared anymore.What the hell?

Sounds to me like something's wrong with the dump of the Shiny Pichu ROM used to give you the Shiny Pichu in your game. Like maybe an error or something.

Hmm I guess it might be because I patched my rom a few times and then switched from japanese to us version.But it's annoying because it won't let me do the event again, so now I have to use PokeSav to get a new spikey-ear.