@DNSB and Jackie_W
I actually tried that on one of the books that opened to the last page and closed again, to no avail. Then my Mini reset itself a couple of times IIRC and it hasn't happened since.
Prior to that it even happened on a short story with no cover or TOC.
I believe that this was 2.3.2 or 2.3.1 and I was having no sleeping cover problems as well
It was several months ago, so I am not absolutely sure but I think a random reset fixed the problem, but it could have been a firmware update.
Neither my Aura or mini seem to reset themselves as often these days, so that is a good thing