What did you put in the bookshelf field? You should have "authors", or "#myshelves,authors" if you are using the two columns.
The values used in the field are the "lookup name". For custom columns, this always has a "#" at the start. Standard columns don't. To see the lookup name for a column, put the cursor over the heading of the column in calibre. A tooltip will be displayed with the lookup name.
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