After displaying a Saves list, it is possible to add a private note to a Saved post or "unsave" the post from the Saves list:
Both of these actions are fine and create no issues.
However, after adding a private note, the "unsave" action becomes a little unsafe because not only is the post "unsaved" from the Saves list, but the private note is also deleted. Naturally, the "Edit private note" and "Delete private note" actions are fine.
We can argue that "unsaving" a post here and simultaneously deleting a private note is not an issue because, after all, the user can see the private note under the post clearly on a yellowish background.
However, this is not the case from the post itself. Clicking on the Saves icon next to the voting buttons unsaves the post from its Saves list and deletes any private note attached to it without any warning. This is unsafe.
New functionality to the Saves feature has already been proposed in this feature request and this suggested improvement which would probably make this problem less likely, however inadvertently deleting private notes is probably a more serious issue and could be considered to be a bug.