[stumped]

well I reproduced it.
the book I used for this test is A B C - by Samuel Delaney, a book that has never been on the tablet.
grabbed it via content server , opened it, went to chapter one of 1st story ( A )
exited, opened moon - imported books to shelf, which scanned the download/cc location and imported it.
opened book and moved to chapter 1 of story B.
closed it- i.e. exiting both the book and moon reader
went back to CC and opened the book again from there - I was back at story A
[ i had not actually forced an exit from cc beforehand ]
so there's for sure some last page location caching going on somewhere under he bonnets!
one more time around. this time I opened via CC, got book a, completely exited book AND cc, went back in via Moon + shelf - was back in book B !

so please look again, and look closely at the "shelf" mechanics in Moon if you can - thanks.
my app versions are whatever is in google store as at today
on the shelf in moon I am seeing 40% read, which matches being on story 2 of 3.
CC says the full path is /storage/emulated/0/download/cc
moon says the path is /sdcard/download/cc
but that's another way of describing the same location I think. I do have an actual SD card but neither app is set to use it, and when I poke around in ES file explorer, both those paths lead to the same place ?
I can prove that another way. I go to CC and choose to delete the book, then I go back to moon and try to open it from the shelf - I get file does not exist.