It would seem (as I'm sure you're all well aware) that the 2.0 Seasonal Items are bugged and cannot be stored in the Armoire.

The following items Cannot be stored:
Moogle Cap
Helm of Light
Summer Morning set (Female, top and bottom pieces)
Striped Summer set (Male and Female, top and bottom pieces)
Summer Evening set (Male, top and botom pieces)
The Wailing Spirit
The Howling Spirit