"Icon theme * not found." message when the icon theme is found

Glax

I'm setting up an application, I'm adding custom search paths for the icon theme, and setting the icon theme.
Icons are loaded just fine but I get the message about the theme in stderr

This is the code in my main:

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    AppInfo& info = AppInfo::instance();
    app.setApplicationName(info.slug());
    app.setApplicationDisplayName(info.name());
    app.setApplicationVersion(info.version());
    app.setOrganizationName(info.organization());
    app.setWindowIcon(QIcon(info.data_file("icon.svg")));

    QStringList search_paths = info.data_paths("icons");
    search_paths += QIcon::themeSearchPaths();
    QIcon::setThemeSearchPaths(search_paths);

    QPalette palette = QGuiApplication::palette();
    if ( palette.color(QPalette::Button).value() < 100 )
        QIcon::setThemeName("icons-dark");
    else
        QIcon::setThemeName("icons");

    GlaxnimateWindow window;
    window.show();
    return app.exec();
}

The message in stderr:

Icon theme "icons" not found.

It seems to be output by app.exec();.
I'm able to use QIcon::fromTheme and get a pixmap from that icon in main before exec() and that doesn't cause the message, so I assume it isn't caused by QIcon.
The message doesn't appear if I use one of the system icon themes in setThemeName (I'm on Kubuntu - KDE).

Having spurious messages in stderr bothers me so I was trying to find what's causing it. If anyone has ideas it would be great.