Broken: version: 2.80 (sub 58), branch: blender2.7, commit date: 2019-04-21 20:30, hash: rB797539e76ccf
Right-clicking on the navbar of the User Preferences only shows the context menu when clicking on the category buttons.
Right-clicking the navbar's background does nothing.
Less relevant, but right-clicking on the Save Preferences button doesn't show the Navigation Bar sub-menu.
Compare with the Properties editor, which also features a similar navbar, but right-click behavior is consistent and always works as expected.