When the latest Marvel Movie Select figures from Captain America Civil War were unveiled by Diamond Select back at Toy Fair there were immediate questions asked due to the display having one appeared to be a four piece connected base - yet only three figures were down for release. Diamond, when asked, confirmed there were only 3 characters.
While us UK fans are still waiting for our supplies, our friends in the US have received their Cap, Mk46 Iron Man and The Winter Soldier - and it is evident that when the three are combined there is a clear "missing piece" from the Avengers Facility Display Base. There are various conspiracy theories around this, the most common (and plausible) is a cancelled figure. When one US fan contacted Diamond the response was that to complete the base at present fans had to buy a 2nd Winter Soldier and reverse the back section.
But it seems Diamond have a potential surprise for us in a couple of weeks as per this message that went onto the Fwoosh forum by Diamond Select representative MSWord
"There will be info about additional diorama pieces revealed in mid-September, probably before your question sees print. There will be a place to get another wall and base, which you can use to add a fourth section to the diorama. Details were being worked out, or I would have said something sooner."
The most likely solution is a Disney Exclusive release, these are always held back from any advance discussion and simply landed in store. This could be a new figure, or simply a tweaked / unmasked version of one of the current 3 figures. I guess time will tell.