I've updated maps twice with Mazda Toolbox with no issues, but this time, my original SD card wouldn't open in Mazda Toolbox (both windows and the toolbox thought it was set to write protect). Between ejects, write-tab shifts, reinserts, having the tab fall out of the slot, trying tape over parts of the notch, etc.I was never able to get either Windows or Mazda Toolbox to allow me to add/delete files from it, so I copied it all over to a new SD card (8 GB Class 4 Kingston).
Two of the files wouldn't copy (corrupted), but Mazda toolbox recognized the mostly complete clone and allowed me to proceed with the 2018 update. Because of my issue with the original card, I went into the diagnostics to double check the new card.
At first I thought it was an issue with the validator, since the new card shows as valid when it has a restored 2017 map on it, but invalid with a 2018 map, but now I'm thinking it might have been a corrupted download. I tried using the card in the car, and navigation loaded, but no streets or roads were showing, just terrain and state names/borders. After trying the same process with another card (16 GB Class 10 SanDisk) and getting the exact same results (valid/invalid card results depending on map year, and no streets/roads showing in nav in the car) I deleted the apps/roaming map files to force a new download of the 2018 map update, and installed the freshly downloaded update on both of the cards. I didn't go back to diagnostics to revalidate either card (it was late and the process had taken hours at this point, and I was paranoid that the validator might actually be messing up the files on the card once it thought it was invalid), so I just stuck the 16 GB card in the car, and haven't had any problems using it.
Curiosity will get the best of me in a few days, and I'll probably try to validate the 8 GB card again (now a backup since the original card is toast) just to see if I get the same error. For now it doesn't appear to matter, since the Toolbox and the car both allow the card to be used.