After updating your application to the 1.1 version, a new function permitting to choose between enabling Miiverse screenshots and using the Picture tool will be featured.
This new function is to be set when making a new canvas.
Unfortunately, posting screenshots from canvas made before installing this update will be automatically disabled.
Other minor bugs and have also been revised.
If you do not plan on posting screenshots to Miiverse, it is absolutely not necessary to download this update.
After installing the update, take a look at the manual on page 6 to learn more about the new option.