I had a very similar problem with my EZ Flash 4. I think the internal battery died on the chip (before I even got it), so the save data was not being retained, yet the cartridge would still try to save when it powered up - and basically it would write a blank save and delete all my progress.
I figured out that the cartridge holds some charge for a short amount of time after powering off, so if you quickly turn it off and on again then the data is still safe and can be written to the sd card properly. So the method was to quickly turn the system off and then back on, wait for the saver to finish, turn the system off. But then the cartridge would still try to save the next time you turn the system on and this would be a blank save... So I put it to manual and now when I start up the system and bypass the saver, play a game, quickly turn the system off and back on, wait for saver to finish, turn system off. A bit of a pain really (but I don't want to have to mess around with replacing the battery).
Essentially the problem is that the save data was lost and yet the cartridge would still save a blank file, so you lose not only your recent progress but the entire save.
It sounds exactly like what's happening here. Watching the castlevania video posted earlier in the thread he lost his save data when he quit without saving (no new save data), and the next time he loaded the save was blank (empty save was written)... Seems to me like the device saved "properly" but there was no save data to write so it saved a blank file.
So the problem could be that it still saves even when it doesn't have any save data?
You can test this by (without using the save dump shortcuts):
Just starting a game with a save and power down without loading or creating a save. (repeat a few times)
Then try starting a game with a save and load the save before powering down. (again repeat this process)
Lastly start a game and save in game before you power down. (and repeat)
The first two tests should always skip the saving process and leave your data intact, otherwise the saver is faulty. The last test should always overwrite the save with a fully functioning save. If all of these work as they should then I think it's safe to assume the save dump shortcuts may be to blame (do they delete the save data on the cartridge after dumping to the SD? And then the power down save tries to dump that data again even though it had been deleted?).
The issue could be avoided in software by checking whether the save is blank before overwriting the old save, and skipping the save whilst telling the user that the save is corrupt. Or moving the old save to a backup location before overwriting. Both methods should probably be optional.
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Also I just read that using a shortcut to save, returning to the software and saving in a second game makes sure that the save is kept (but the second game save risks being blanked), or using a shortcut to save and then pulling out the cartridge also makes sure that the save is intact. I believe this confirms my suspicions that the saver is trying to save even when there is no save data on the cartridge.
