My K3 (arrived beginning of September) functioned perfectly but was stolen, along with its cover, in a London pub in December. I got a new one and new cover on 24th December and it seems to have difficulties of this type. I did lots of resets and finally rang Amazon this morning. They advised removing the cover and then doing a reset. So far it appears to have worked.
The actual problems were an inability to stay in sleep mode and losing my place in a book.