Change KmessageBox::detailedError dialog type to KmessageBox::error for a better view.
When the dialog is created the details are hidden. The detail text is not that long that it couldn't be shown directly.
More, the new dialog box could be ::sorry, it changes the caption from "error" to "sorry" and the icon from the red error to the yellow warning
FIXED: [ 383567 ] Details section is empty in 'Do not know which files to compare.' window