I do not seem to be able to select the CD to copy from the combo-box on the copy disk dialogue window - I have tried with a mouse and keyboard but can't select the disk if there is only one item in the menu :( Any suggestions?
That's this bug, which although it shows as fixed I ran into with a brand-new Linux Mint 16 installation just now. (Linux Mint is derived from Ubuntu.)
The good news is, if there's only one item on the list, just go ahead and choose your target (I was doing an .iso file) and click Create Image. It uses the one item on the list, despite it not showing as selected.