I found a bug in label fields: if you insert an apostrophe in label text (the ' character) it will be escaped as \' in wordpress backend menu and in the list of custom post types.
Moreover if you go to edit the label, you see it escaped in the text field and if you save without removing the backslash, it is escaped again and show as \\\'.
I use "Nations' pages" (without double-quotes) as label. On menu appear: "Nations\' pages", ad if I go to edit the label, in the input text I find: "Nations\' pages". Then I save as is and it becomes "Nations\\\' pages".