Hey emmakpark, you’re right – this is a bug! Found it and just pushed a fix.
The issue: the story detail pane had a click handler that was force-marking stories as read, completely bypassing the “manually mark as read” preference. So no matter what you had that setting set to, clicking anywhere in the story content would mark it as read.
The fix is live now. With your preference set to “Manually by hitting m or u”, clicking on stories and interacting with them should no longer mark them as read. Only pressing m or u will toggle read status.
Let me know if you’re still seeing the issue.