What changed
Quiet period 2 s → 20 s. A background save now only happens after the cart RAM has been untouched for 20 seconds, so ordinary in-game writes during active play no longer trip it. A real menu save is followed by a pause, so it still gets written.
Checksum guard. Before any save, background or on-quit, the live cart RAM is checksummed against what was last written; if the bytes are identical, nothing is written to the card. The game replaying identical state, which is what caused the save-just-after-opening, no longer touches the SD card at all. Seeded from the loaded .sav at launch, so opening a game and idling never writes.
pelgraine