When editing a library which has OpacLibraryInfo defined there is a link in the form "Edit HTML content". The link passes the wrong id parameter, resulting in an incorrect entry being edited.
Equally bad but more confusing, it seems to be the wrong id parameter unless the right one is currently the highest number there has ever been. When you you go to test it in ktd, you have to create an OpacLibraryInfo page, and then you see that your link has the right id, 7. Create another sort of HTML customization page, and now the link is wrongly id 9. Delete that second one, your link is still 9.