When you insert an external PDF-file (e.g. for a table where you have to keep the original layout) into a floating element for give it a caption, the inserted PDF looks nice, but the caption isn't displayed above or under the inserted PDF but anywhere in the PDF (like a second layer). The use of boxes or anything like that doesn't help. (I'm using Lyx 2.0.4 on Windows 7.) This bug should be fixed very soon, because that's not only a bug for better usability but for better documents.