When adding CanDestroy:[minecraft:banner] to an item you're not able to break banners in /gamemode 2
1: Place banner
2: /give @p stick 1 0 {CanDestroy:[minecraft:banner]}
3: /gamemode 2
Try to break the banner, but you will see no hitbox and you won't be able to
Also it says "missingno" instead of "Banner" http://puu.sh/aBCOt/51fb56f041.png
Its either standing_banner or wall_banner.