SUMMARY

QStringList Settings::defaultIgnoreList() in src/core/settings.cpp contains old entries that are hardcoded:

// default values
// A static list of KDE specific words that we want to recognize
QStringList Settings::defaultIgnoreList()
{
    QStringList l;
    l.append(QStringLiteral("KMail"));
    l.append(QStringLiteral("KOrganizer"));
    l.append(QStringLiteral("KAddressBook"));
    l.append(QStringLiteral("KHTML"));
    l.append(QStringLiteral("KIO"));
    l.append(QStringLiteral("KJS"));
    l.append(QStringLiteral("Konqueror"));
    l.append(QStringLiteral("Sonnet"));
    l.append(QStringLiteral("Kontact"));
    l.append(QStringLiteral("Qt"));
    l.append(QStringLiteral("Okular"));
    l.append(QStringLiteral("KMix"));
    l.append(QStringLiteral("Amarok"));
    l.append(QStringLiteral("KDevelop"));
    l.append(QStringLiteral("Nepomuk"));
    return l;
}

Those are visible in the systemsetting module and can be removed but are instantly there when the systemsettings is re-opened.

The function is only used in
QStringList Settings::defaultIgnoreList() in src/core/settings.cpp contains old entries that are hardcoded

// default values
// A static list of KDE specific words that we want to recognize
QStringList Settings::defaultIgnoreList()
{
    QStringList l;
    l.append(QStringLiteral("KMail"));
    l.append(QStringLiteral("KOrganizer"));
    l.append(QStringLiteral("KAddressBook"));
    l.append(QStringLiteral("KHTML"));
    l.append(QStringLiteral("KIO"));
    l.append(QStringLiteral("KJS"));
    l.append(QStringLiteral("Konqueror"));
    l.append(QStringLiteral("Sonnet"));
    l.append(QStringLiteral("Kontact"));
    l.append(QStringLiteral("Qt"));
    l.append(QStringLiteral("Okular"));
    l.append(QStringLiteral("KMix"));
    l.append(QStringLiteral("Amarok"));
    l.append(QStringLiteral("KDevelop"));
    l.append(QStringLiteral("Nepomuk"));
    return l;
}

Those are visible in the systemsetting module and can be removed but are instantly there when the systemsettings is re-opened.

The function is only used in
src/core/settingsimpl.cpp:    const QStringList ignores = settings.value(ignoreEntry, Settings::defaultIgnoreList()).toStringList();

so only returning an empty default (initial) list is the desired behavior.

STEPS TO REPRODUCE
1. Open Systemsettings, spellchecking
2. see the list hardcoded above, remove items
3. re-open systemsettings, entries are back


OBSERVED RESULT
Filled list with constant values

EXPECTED RESULT
Empty list

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: 6.0.0
(available in About System)
KDE Plasma Version: 6.0.0
KDE Frameworks Version: 6.0.0
Qt Version: 6.6.2

ADDITIONAL INFORMATION

The error is also visible in all versions back to kf5, so it (should) be removed there, too.