When creating or opening two or more projects in K3b, only the first project tab show the filename column. All subsequent ones only show type and size columns.
This happens with both Oss and packman versions.
There’s no bug report on this at kde.org, at least since the end of 2016.
Deleting ~/.config/k3brc resets the interface settings but the problem persists.
Changing the default app style from breeze (the default, I think) to Oxygen fixes the problem. Tested with both Breeze and Oxyzone desktop styles, so I’m thinking this may be an openSUSE issue, not KDE.
Perhaps a bug report is in order.