That is a known and well discussed problem with FW2.3.1. It is still there in 2.3.2.
There hasn't been an official release of 2.3.2 outside of Japan. But, you will probably be safe with 2.3.2 on your Touch. I have run it for a few weeks with no problems. My Touch was definitely one of the problem ones. Kobo have done something, I suspect via FW2.0.4, that changed these devices so that the later firmware install OK even if you need to do a factory reset.