SUMMARY STEPS TO REPRODUCE 1. Copy a some files. Some of them need to be in the destination already; 2. Open another window, like Firefox. OBSERVED RESULT The confirmation dialog will steal the focus and if you skip or overwrite a file, the previous window won't be restored. EXPECTED RESULT Maybe a notification could appear in the system tray to confirm the operation or the Dolphin icon in the taskbar could be displayed with a flashing orange background. SOFTWARE/OS VERSIONS ADDITIONAL INFORMATION I'm using the "medium" focus stealing prevention.
It it didn't steal focus, you would miss it, and the copy job would be silently stuck there for until you did notice it. It could be hours. If you hate focus stealing, there are a variety of focus stealing preventiion settings in System Settings > Window Management > Window Behavior >
A notification in the system tray would be less disrupting. Sometimes focus stealing is great for something really critical.