Quote Originally Posted by djr33 View Post
On a Mac, you can choose whether you want to save a file or copy to the clipboard. The settings are somewhere in the System Preferences-- if anyone can't find it, I can check, but it should be fairly obvious. The disadvantage of that is that you have to remember a few more key combinations. On Windows it's simple!
OR, you can just press command+shift+3 and it automatically saves to the desktop

As to the issue, does the print-screen button perform any other function at any time normally? Maybe you had a key stuck that caused it to do something else? Have you fiddled with your keyboard shortcuts recently?

Also, since this is a desktop, try with different keyboards, see if you can replicate the incident.