Here's the way you can take a screenshot of a remote desktop:
1. In the Full Control or View window click on the program icon in the top left corner of the window, where the title is.
2. In the menu, select 'Send key' -> 'Print screen'.
3. Grab the screenshot from the remote PC by clicking on the 'Get remote clipboard' button on the pop-up toolbar.
Now the screenshot is in your local PC's memory and you can save it just as you normally do on Windows (e.g. paste it into Paint and save as jpeg file).
We'll see if we can do something more quick and convenient about taking remote screenshots in the future releases.