I have recently purchased some apps from the app store and after downloading them, the icon that appears in the dock changes to a different icon. It is now the same icon appearing on all newly downloaded apps. Does anyone know what is happening here?

I have recently purchased some apps from the app store and after downloading them, the icon that appears in the dock changes to a different icon. It is now the same icon appearing on all newly downloaded apps. Does anyone know what is happening here? Even updating an older game app resulted in the original game icon changing to the new identical icon that all new apps are appearing with. This new icon is like a page with a ruler, pencil and paintbrush. Any tips on how to stop this or how to revert to the icon as it appears on the app store would be appreciated.