What's this slidery thing next to the download link?
When the slider is in the ON position clicking the download link will download the craft and open the download tab so show you more info
When the slider is in the OFF position clicking the download link will just open the download tab without downloading the craft
Once you've downloaded a craft the slider will automatically move to the OFF position, so you can then open the download tab without re-downloading the craft each time.
If you want to re-download the craft there will be a link in the download tab
It also acts as a visual que to remind you which craft you've already downloaded, if it's in the OFF position (red) you've already downloaded the craft.
As you are not logged in it will only remember what craft you've downloaded in this session.
if you want KerbalX to remember your downloads between sessions.