It is a 2.3.1 bug, seems to be fixed in firmware 2.3.2. Unfortunately 2.3.2 hasn't been officially distributed outside of Japan yet, so sideloading firmware might be the only way to get the bug fix.
If you sideload firmware 2.3.2 be very careful, there are two different types of Kobo Touch, one uses the Touch firmware and the other uses the Glo/Mini firmware. I don't know how to tell which is which, maybe someone else can help with that. (I have a Glo only).