"Copy to computer/ereader" not working under "file" but does work in library

(Note: I'm not using an English version, so some of the menu items may have different names than what I assume they are...)

In Adobe Digital Editions I was confused because when I selected a book and wanted to copy it to my ereader the "copy to computer/ereader" item under "file" didn't allow me to copy it. The ereader was greyed-out. However, in the Library overview using the right mouse button to get a pop-up, the same menu item did allow me to copy to the ereader.

Why the difference? I've - finally, after a frustrating hour - found a way to do it, but why doesn't the for me intuitive way of navigating to the ebook and then selecting an action on it in the "file" menu not work?