In the Add New Page & Edit Page screens, the Parent dropdown in the Page Attributes palette is expanding to the right. The left side of the pulldown options align with the left side of the palette. This means, that when a page title is long, the scroll bar can be offscreen.
(In contrast, in the quick edit screen, the parent pulldown expands to the left, ensuring we can always see the scroll bar on the right.)
As discussed here, the scroll bar can be made visible if the user resizes his window display. But I wonder if, in a future WordPress version, the CSS of the palette could be altered to accommodate.