STEPS TO REPRODUCE
1.  On the menu, View->Save tab layout to file
2. Enter a filename and click OK

OBSERVED RESULT
File contains simply
{
    "Orientation": "Horizontal",
    "Widgets": [
        {
            "SessionRestoreId": 0
        }
    ]
}
no matter how many tabs are open.

EXPECTED RESULT
File should contain at least some data that could be useful for restoring them (without invisible local Konsole state that might be wiped on a clean OS reinstall)