Yeah, for me as well. It's normal.
I zapped the kf8 folder, and opened each of the 2 books on device (one of them side loaded), reconnected to USB.
kf8 folder is back, with 3 files, two small files without file extensions and one with same name with .settings extension. The latter is just a text file with '|' delimited values.
But there were 37 + 2 (.settings) files in there before, ranging in size from 4Kb to 1Mb. Not nothing, but not a lot.
So my conclusions are:
- yes, safe to delete.
- Created as result of normal operation of Kindle.
- And probably contents do not expand beyond a certain point, as that is normally how cache works.
- I suspect it helps load previously opened books open faster on subsequent opens.
I looked at another Kindle, oldest file was created June of last year and there are 140 files in there. I have had this Kindle longer than that, so I take this as evidence that things do not persist in there forever.
Kindles are notorious for leaving crumbs behind even after downloads are removed.
But I'm afraid my life will never be the same after this. it's always going to bother me just a little bit knowing my Kindle has digital dust in it.