I believe it would be very useful to be able to set item arrangement for folders discretely. For example, it would be good to have global item arrangement by name, and item arrangement for the "Downloads" folder by modification date.
So there must be a division into global item arrangement somewhere in Thunar's options and individual item arrangement for every folder, which overrides the global one when set.
This solution would be perfect both for users who like global item arrangement (they just won't need to worry, nothing will change for them, except that global item arrangement will be changed from Thunar's options instead of context menu) and the other users (whom I believe to be a majority).
Thanks for reporting! Yes, would be nice to have that ... bug already exists.
*** This bug has been marked as a duplicate of bug 3521 ***