I use Post Type Switcher in my website, where I use the Dashboard Site Notes plugin too. This plugin create a new dsn_note custom type. When I try to update a previous published Site Note, automatically it is changed in a classic post. I saw that this problem disappear when I switch Post Type Switcher off, so I think it's a bug related to your plugin. The dsn_note custom type is invisible, so in that kind of post Post Type Switcher must not appear at all.