I've had this issue in the past. For me, it occurred when I had code where some lines had hard tabs and others had spaces (this is a common artifact when editing other peoples' code). Then doing column-mark-and-delete can actually delete the first character of un-marked data on *some* of the lines, which makes recovery quite interesting. Also, undo doesn't always properly restore things.
-- <https://forum.pspad.com/read.php?2,69589,69610> PSPad freeware editor https://www.pspad.com
