Missing data in csv file

[Yrsa]

Does anyone know why there is missing data in the csv file when exporting a library?
What I am missing is "Date Read", the days I completed reading a book. I cannot find a pattern in which books are missing this date. Sometimes it is for books that I have read more than one time, sometimes it is books I have read once.
Has anyone else had this problem? Does anyone know why this is happening?

[Yrsa]

Some further investigation leads me to believe that the dates go missing if a person changes the date in the review mode (either chooses the date or presses the "set to today"-button. The date is in the csv file when one mark the book as "I'm finished!" in the update progress function on the start page. If one tried to change the date after pressing the "I'm finished" --> the date appearing in the csv file is wrong.