Signal QTextDocument::contentsChanged() is sent twice on each backspace deletion

Signal QTextDocument::contentsChanged() seems to be sent twice on each backspace deletion.

You can easily reproduce this e.g. with Qt textedit demo by:

1) adding one more signal connection to TextEdit::TextEdit(QWidget *parent) contructor:

connect(textEdit->document(), SIGNAL(contentsChanged()), this, SLOT(showSignalCount()));

2) creating an own slot for setting a debug breakpoint there when using backspace:

void TextEdit::showSignalCount() {}