QTextCharFormat setFontUnderline does not sets the attribute to document

If setFontUnderline() is set and then it is merged with QTextCursor then underlying attribute is not available in document.
Attached example can be used to see this behavior.
Steps:
Run the application on a certain timer
It will underline the text
then on another timer it will remove underline
But in finaly when text is shown using doc it still shows underline text.