Don't power off?
I have seen that a couple of times after a firmware update. But, after going to any other screen and returning, it is fixed permanently.
Other than that, my first thought is a corrupt database. The power-off should force a write and read of the database, but if there is a problem with the database, the write might not happen and it is reading an unchanged database. You can do a check on the database to see if it has a problem.
The only other thing I can think of is the "Kobo Reader.conf" file. This has some options about what gets shown at restart or disconnect. They should get changed so that they only happens once or once per firmware version. If something is preventing this file from being updated, then it could do what you are seeing. But, the only likely reason for this is if the file system is corrupt.