Set button invisiable on a plugin, will cause page scroll to top?

[hcfalan]

I have build a chat application, based on QT widgets. For display message in list, I choosed QWebView, because the message data will text, image, audio, file transfer. For display file transfer message, I use 'object' tag in html, and custom a plugin named 'TTFilePlugin' which extends from QWidget.
message-display.jpg
The layout of TTFilePlugin should be like this:

void TTFilePluginUi::setupUi()
{
    QRect rectIconLabel(0,0,48,48);
    mIconLabel = new QLabel(owner);
    mIconLabel->setGeometry(rectIconLabel);
 
    QRect rectNameLabel(rectIconLabel.right() + 10, rectIconLabel.top(), 100, 24);
    mFileNameLabel = new QLabel(owner);
    mFileNameLabel->setAlignment(Qt::AlignLeft|Qt::AlignTop);
    mFileNameLabel->setGeometry(rectNameLabel);
 
    QRect rectSizeLabel(rectNameLabel.right() + 10, rectNameLabel.top(), 60, 24);
    mFileSizeLabel = new QLabel(owner);
    mFileSizeLabel->setAlignment(Qt::AlignRight|Qt::AlignTop);
    mFileSizeLabel->setGeometry(rectSizeLabel);
 
    QRect rectProgressBar(rectNameLabel.left(), rectNameLabel.bottom() + 4,
                          rectNameLabel.width() + 10 + rectSizeLabel.width(), 20);
    mProgressBar = new QProgressBar(owner);
    mProgressBar->setTextVisible(false);
    mProgressBar->setGeometry(rectProgressBar);
 
    QRect rectRecvButton(rectIconLabel.left(), rectIconLabel.bottom() + 5, 60, 30);
    mRecvButton = new QPushButton("Receive", owner);
    mRecvButton->setGeometry(rectRecvButton);
 
    QRect rectOpenButton(rectRecvButton.right() + 10, rectIconLabel.bottom() + 5, 60, 30);
    mOpenButton = new QPushButton("Open", owner);
    mOpenButton->setGeometry(rectOpenButton);
 
    QRect rectSaveAsButton(rectOpenButton.right()+10, rectIconLabel.bottom() + 5, 60, 30);
    mSaveAsButton = new QPushButton("Save As", owner);
    mSaveAsButton->setGeometry(rectSaveAsButton);
}

void TTFilePluginUi::setupUi()
{
    QRect rectIconLabel(0,0,48,48);
    mIconLabel = new QLabel(owner);
    mIconLabel->setGeometry(rectIconLabel);

    QRect rectNameLabel(rectIconLabel.right() + 10, rectIconLabel.top(), 100, 24);
    mFileNameLabel = new QLabel(owner);
    mFileNameLabel->setAlignment(Qt::AlignLeft|Qt::AlignTop);
    mFileNameLabel->setGeometry(rectNameLabel);

    QRect rectSizeLabel(rectNameLabel.right() + 10, rectNameLabel.top(), 60, 24);
    mFileSizeLabel = new QLabel(owner);
    mFileSizeLabel->setAlignment(Qt::AlignRight|Qt::AlignTop);
    mFileSizeLabel->setGeometry(rectSizeLabel);

    QRect rectProgressBar(rectNameLabel.left(), rectNameLabel.bottom() + 4,
                          rectNameLabel.width() + 10 + rectSizeLabel.width(), 20);
    mProgressBar = new QProgressBar(owner);
    mProgressBar->setTextVisible(false);
    mProgressBar->setGeometry(rectProgressBar);

    QRect rectRecvButton(rectIconLabel.left(), rectIconLabel.bottom() + 5, 60, 30);
    mRecvButton = new QPushButton("Receive", owner);
    mRecvButton->setGeometry(rectRecvButton);

    QRect rectOpenButton(rectRecvButton.right() + 10, rectIconLabel.bottom() + 5, 60, 30);
    mOpenButton = new QPushButton("Open", owner);
    mOpenButton->setGeometry(rectOpenButton);

    QRect rectSaveAsButton(rectOpenButton.right()+10, rectIconLabel.bottom() + 5, 60, 30);
    mSaveAsButton = new QPushButton("Save As", owner);
    mSaveAsButton->setGeometry(rectSaveAsButton);
}

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After page loaded, I scroll to page end to make file transfer message appear. when i click the 'Receive' button on TTFilePlugin, the page auto scroll to Top!

The slot code of 'Receive' button clicked signal fired like this:

void onReceiveButtonClicked() {
  ui->mReceiveButton->setEnabled(false);
}

void onReceiveButtonClicked() {
  ui->mReceiveButton->setEnabled(false);
}

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If I comment the line 'ui->mReceiveButton->setEnabled(false);' and try again, the page will NOT auto scroll to top. Why?