This appears to still be an issue.
When selecting Settings > Theme > Screensavers, the Photo Streams icon, then Set as screensaver.
Then, selected “Preview (current screensaver)”. It briefly shows a full-screen purple Photo Streams logo screen, then returns back to the Photo Streams settings page. Nothing happens. Doing the same with another screensaver works fine/as expected.
Uninstalled the Photo Streams app, checked for system updates (none), restarted system, reinstalled Photo Streams - same result
OS: 11.5.0, build 4312-50
model: 3810RW