People have indicated they thought a pet may have jumped on their reader. On a bedside table it's also quite possible to whack it in your sleep or just squeeze it too hard if you have a restless night or dream of Kobo programmers chasing you while trying to upgrade your firmware against your will...
Nooooooo, not new bugs!
Good luck getting the issue resolved, it could very easily be a manufacturing issue where undo stress was applied at some point in the manufacturing or assembly processes and manifested itself later. I believe there were a number of these issues with the last new e-ink screens when they first debuted(Touch & Kindles), could be again as the screens in the Glo are fairly new to market and the Glo has not been out all that long. Hopefully Kobo can afford to take a hit for a customer every now and then since proving it one way or the other would seem impossible.