https://www.wowhead.com/item=168059/ensemble-restless-dreambound-battlegear
Chest is hidden but I have it

https://www.wowhead.com/item-set=1185/barbed-assassin-battlegear
Head & shoulders is hidden but I have it

When I chose "hidden" set my https://www.wowhead.com/item=171333/renowned-explorers-rucksack is still showing

And here is another little bug:
When I enable "Appearance Preview" and enable "Use custom model - Human Male" I got black character model

V1.9.1
ruRU wow client

I'll look into 1 & 2.

3 is from me missing adding the "hidden cloak" id. It should be fixed in the next update

4 The custom race/sex currently uses a "Transmog Model" that uses that dark skin because Blizzard broke something in a previous patch so when you change the race/sex it does not update the character skin so you get a really broken looking model. Im hoping that the prepatch fixes it. I'll probably should add a note on the options screen about it.