I have also recently bought an Ereader Pro + and note the same problem. yesterday I re-opened the case and found the book I was reading had advanced to the end. Finding where I had left of wasn't easy
It appears you need to put the reader in standby before closing the cover. As a Kobo Glo user where closing the cover puts the reader in standby this has come as a bit of an annoyance.
BobC