Full Idea
If a globally intrinsic properties are those that never vary between duplicates across possible worlds, then necessarily coextensive properties will either be both intrinsic or both extrinsic.
Gist of Idea
Global intrinsic may make necessarily coextensive properties both intrinsic or both extrinsic
Source
comment on David Lewis (On the Plurality of Worlds [1986], p.61-2) by Ross P. Cameron - Intrinsic and Extrinsic Properties 'Analysis'
Book Reference
'Routledge Companion to Metaphysics', ed/tr. Le Poidevin/Simons etc [Routledge 2012], p.268
A Reaction
Presumably this problem would arise if some intrinsic property entailed an extrinsic property (or, less likely, vice versa). These sorts of problems arise when you try to define everything extensionally (even across possible worlds).
Related Idea
Idea 15397 If a global intrinsic never varies between possible duplicates, all necessary properties are intrinsic [Cameron on Lewis]