I was not sure on how to reply till you mentioned that. What it sounds like is what happened to my AntiX 8.5 frugal persistent install on my 4 gig SD card one time when it was unmounted improperly.sdb1 have frugal installs?
What I did to fix it was. I had to insert the card into my Ubuntu 10.04 LTS IBM M57 Desktop with a USB to SD adapter. Then when it mounted. Looked in Gparted and card showed it was maxed out with written Data.
I umounted it in Gparted using right click menu and then again right clicked in Gparted and ran Check from the Menu. When done and Gparted rescanned the SD card. My partitions (Ext2), / and /data were shrunk from showing as being full of data. Card booted up properly again. Before it would not.
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I now run AntiX 8.5 Full Iso on my EEEPC 701SD 8 gig SSD and Puppeee 4.X Beta frugal persistent runs on my 4 gig SD card now . Hope that explains what might have happened to you.
Edit: P.S. What I do now is I copy over my personal pupsave over to AntiX /home on internal SSD as a backup. Kinda reverse of what you do