Email view switches to Unread from user-defined folder without user action

I've noticed a change in behaviour in the webmail interface and I'm trying to understand what's going on.

When I'm viewing emails in a user-defined folder, the view sometimes switches to the Unread folder without any action on my part. I'm not clicking anything or navigating away; the screen simply jumps to Unread.

This is disruptive, as it breaks the flow when working through messages in a specific folder.

A few questions:

• Is this a recent change or a new feature in the web interface?
• If so, is there a way to disable it and keep the view fixed on the selected folder?
• Alternatively, could this be caused by a setting I may have changed unintentionally? If so, which setting should I check?

Thanks in advance for any clarification.