You know about the App Inventor Backpack?
You can drag blocks into the “Backpack” icon at upper right of the MIT App Inventor Blocks editor. Once in the backpack, you can later drag items out of the backpack providing a nice way to move blocks around or between apps.
Until recently, the backpack was automatically emptied when you exited App Inventor. But … that has changed recently!
A couple of months ago the Backpack behavior was changed so Backpack content is persistent. That means the backpack retains a copy of your blocks even when you exit App Inventor.
This makes it easier to move favorite code blocks between apps or apps you download from the MIT Gallery.
To empty the backpack, you need to right-click (Ctrl-click on a Mac) somewhere in the whitespace (background) and then select Empty the Backpack from the pop up menu.