My problem was a bad install of something, so I just uninstalled. It may be that I never had it before because I have the
advancedwifilockfree.apk app installed (no need to mess with settings).
This is a known issue with Android 2.3.3, btw. Kobo may have a work around to give us, but it is not really a Kobo thing, from what I can tell. No guarantees that the app does the trick, of course, because there can be other causes (like there was for me).