It's just come to my attention that something is going glitchy with at least one of my local folders. I had created a folder for my hydro bills. As soon as my hydro bills come in as email (IMAP), I drag them to a local folder entitled "Hydro." Tonight, I did as I usually do, except this time I checked the local folder. I only found May's Hydro bill. And there should be at least 6 in there. The one I just dragged their tonight simply vanished. Though the messages appear as duplicates, the dates are not, as well as the invoice, obviously. This isn't right. I've lost a number of invoices now, and I thought dragging to a local folder is safe. Huh?

Should be safe. Try rebuild?
I've had glitches sometimes when I was in 10.5