Selection of formatted text in QPlainTextEdit with SyntaxHighlighter changes format

class InputLine::TriggerHighlighter : public QSyntaxHighlighter
{
    InputLine &input_line;
public: 
    double formatted_text_length;
    bool block_rehighlight = true; 
    TriggerHighlighter(QTextDocument *d, InputLine *i) : QSyntaxHighlighter(d), input_line(*i) {}

    // QPlainTextEdit::keyPressEvent triggers rehighlight.
    // At this point trigger_lenght is not set yet.
    // We want to make sure that we are in contol over the rehighlights.
    // Also rehighlight emits QPlainTextEdit:textChanged which has to be avoided.
    // Intended shadowing.
    void rehighlight()
    {
        block_rehighlight = false;
        QSignalBlocker b(&input_line);  // see below
        QSyntaxHighlighter::rehighlight();  // triggers QPlainTextEdit::textChanged!
    } 
 
    void highlightBlock(const QString &text) override
    {
        if (block_rehighlight)
            return;   
        block_rehighlight = true;
        formatted_text_length = 0.0; 

        // Needed because trigger length is set async and may exceed the text length
        const auto highlight_length = std::min(input_line.trigger_length_, (uint)text.length());     
        if (highlight_length)
        {
            auto f = input_line.font();
            f.setWeight(QFont::Light);
            f.setCapitalization(QFont::SmallCaps); 

            QTextCharFormat fmt;
            fmt.setFont(f);
            fmt.setForeground(input_line.trigger_color_);
            setFormat(0, highlight_length, fmt);      

            formatted_text_length +=
                QFontMetricsF(f).horizontalAdvance(text.left(highlight_length));
                setFormat(highlight_length,
                      text.length() - highlight_length,
                      input_line.palette().text().color());
        } 

        if (text.length() > highlight_length)
            formatted_text_length
                += QFontMetricsF(input_line.font())
                       .horizontalAdvance(text.sliced(highlight_length));
    }
};