QTextEdit hangs when large text is copied

When a large text is copy paste  to QTextEdit, it hangs. cant upload sample text file of size 60 mb.

But with following tiny code if large file is copied to clipboard and pasted here hangs forever. this works with QPlainTextEdit

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QTextEdit editor;
    editor.resize(800, 600);
    editor.show();
    return a.exec();
}