为什么select(QTextCursor::BlockUnderCursor）包含额外的垃圾字符

Windows 7 SP1
MSVS 2010
问题4.8.4

我正在使用QTextCursor来获取每个块的文本。我使用select(QTextCursor::BlockUnderCursor)获取文本，然后使用movePosition(QTextCursor::NextBlock)转到下一个块。但是当我再次select(QTextCursor::BlockUnderCursor)时，我在QString中得到了一个额外的垃圾字符，并且锚点已经移动到了前一个块的末尾。

将其用于text.txt：

A
B

此代码的注释遍历问题并提出以下问题：

 #include <QTGui>
 int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QMainWindow*          window = new QMainWindow;
    QTextEdit*            editor = new QTextEdit(window);
    QTextDocument*      document = new QTextDocument(window);
    editor->setDocument(document);
    QFile file("test.txt");
    if (file.open(QFile::ReadOnly | QFile::Text))
        editor->setPlainText(file.readAll());
    QTextBlock block = document->begin();
    QTextCursor* cursor = new QTextCursor(document);
    int pos = cursor->position();           // = 0
    int anchor = cursor->anchor();          // = 0
    cursor->select(QTextCursor::BlockUnderCursor);
    pos = cursor->position();               // = 1
    anchor = cursor->anchor();              // = 0
    QString text = cursor->selectedText();  // = "A"
    int size = text.size();                 // = 1
    cursor->movePosition(QTextCursor::NextBlock);
    pos = cursor->position();               // = 2
    anchor = cursor->anchor();              // = 2
    cursor->select(QTextCursor::BlockUnderCursor);
    pos = cursor->position();               // = 3
    anchor = cursor->anchor();              // = 1 Why not 2?
    text = cursor->selectedText();          // "B" in debugger
                                            // but text.at(0) = junk & test.at(1) = "B"
    size = text.size();                     // = 2 Why? Why not 1?
    return app.exec();
}