In KDE 3, the PrtScr button would initiate KSnapShot (for capturing the screen or parts of the screen).
In KDE 4 this key is assigned to 'print the page' from within whatever application is in use at the time.
Arguably this is a benefit to some users, but it seems like those users could have made the reconfiguration, rather than people used to the status quo having to make it. {sigh}
Work-around
Easy enough.
Run System Settings , then Input Actions | right-click in big empty space on left and do New Global Shortcut | Command / URL.
Call it KSnapshot, enter something useful in the comment (General) field, and set Action-Command/URL to ksnapshot, and then hit the Shortcut button and then hit the PrtScr button - it'll ask if you want to reassign this key, and since you do, you click yes. Easy. Then Apply and you're done.