Extra whitespace accessible with scroll-bars at the end of QPlainTextEdit widget

In case when QPlainTextEdit object is not visible and reacts on some signal which invokes appendPlainText on it, a strange white area is accessible with a scroll-bar at the end of the document. The white area disappears after resizing the window or typing some text or invoking a similar action that requires QPlainTextEdit interactions.

The appended white area looks like this:

The expected behavior of an example app should be like this:

In the attachment, there is a simple app which reproduces the problematic behavior. The button appends text to the end of the document.