Items limited to certain maps

I didn't see if there was already a discussion for this, but I recognised (which confused me at first), that in the tab Item Sets there is for some items the indication that this certain item is not available on a certain map. E. g. Zhonya's Hourglass: "This item is not available on the folloing maps: The Crystal Scar) However I noticed that such an indication is not available for some items such as Wooglet's Witchcap or Moonflair Spellblade which can only be taken on the map Twisted Treeline. I find this quite confusing while arranging an item set for certain Champions.

I just wanted to suggest that the indications for the items could be corrected and it may be helpfull if there was the option to filter the Item Sets list not only by the Starting Items, Tools, Defense, Attack, Magic and Movement, but also by the maps so that it shows only the required items.