Shadowdancer shadow , is mistakenly taking armor attributes.
The shadow does not really wear any armor you are wearing, IE the armor is not contributing to its AC at all.
But if you wear light armor while summoning it - ( And you will because of "lightly armored" feat ) the shadow AC will be reduced because armor penalty to dex )
There is very easy way to circumvent that, by summoning shadow naked. But it seems very lame in RP. When in group you are stripping naked to summon your shadow 
I suggest that as you can save and equip specific weapons on shadow, there should be way to save armor too.
There is no in game benefit. So it will make no balancing issues.
Its just a thing that is quality of life and will be very nice to be fixed