As you may be aware, your 3DS eShop copy of Mutant Mudds now has a free update waiting for installation — this adds the 20 Ghost levels previously included in Mutant Mudds Deluxe on the Wii U; in fact, the update even rebrands your game on the front screen to have that Deluxe title. This is particularly great news in PAL regions, where the expanded Wii U version was never released.
Unfortunately, this update has caused an unexpected bug, which prompted some initial panic that it 'breaks' your save files; it doesn't seem to affect 100% of those that download the update, but did happen to us and a number of others. Your diamond and collectible count may get jumbled in your safe data, and if you'd unlocked the 'Grannie' content, including an extra — particularly useful — playable character, the ability to switch between the two on the front screen is also lost, rendering some extra retro-themed levels inaccessible.
Though Renegade Kid is planning to look into the issue, it seems that these problems are easily resolved by simply beating the first level. Simply access your save file and complete the first Ghost stage — accessed via the mirror in the middle of the screen — and you'll be presented, strangely, with an end credit teaser. Pleasingly, this then fixes your collectible total on that save file and returns the ability to switch playable characters on the home menu screen; all then works as it should.
We're sure that a formal fix will be applied in future, but if your update goes wrong there's no need to panic.
Thanks to James Duckett for the heads up.