Yeah, sadly that was an old Naninovel bug (which has since been fixed at least :3) that shouldn't be a problem once the game is updated. It's just that exporting an update with that fix in isn't an easy task >.<
If it were quick to do, I'd release an update of the demo that fixes that issue + some other UI-related gremlins, but the version of Naninovel that the demo was made in is so incredibly out of date now that any update will break most of the code in the demo T_T
Basically, I will need to start the game from scratch with the latest version of Nani. But I don't feel that's worth doing until there's more actual content to add story-wise. So, for now, the janky demo will have to suffice x3 Sorry aboot that! And cheers for checking it out :3