Problem loading books from Kindle

[MacNala]

Calibre 1.15, Windows 7, UK Standard Kindle.
Recently, probably after installing 1.15, I have been having trouble moving books between my Kindle and Calibre Library.

I purchased two books and had them sent to my Kindle from Amazon via whispernet. They arrived safely and the next time I attached the Kindle to Calibre selected them from the device screen and added them to the Calibre library. At first the books did not seem to appear. I tried again after checking they were still on the Kindle. This resulted in the 'duplicate book' warning.
They library display showed them but did not show them in the device column.

To determine what was going wrong I deleted the books from the Kindle and the Calibre library and then got Amazon to deliver them again. Being very careful of the steps I took I repeated the copying from Kindle to Calibre and the result is the books appear in the library screen with the column labelled device empty.

Can anyone help?