I'm under the impression that the Challenge Mode scaling is supposed to leave Hit alone, and take away from the other stats.
Here are some screenshots of my hit inside a Challenge Mode, and then outside of a Challenge Mode.
1. Inside: http://i.imgur.com/Ayevl.jpg
2. Outside: http://i.imgur.com/SGDbi.jpg
Deleted Cache, removed WTF and Interface
3. Inside: http://i.imgur.com/IscJR.jpg
4. Outside: http://i.imgur.com/x8nk2.jpg
5. Spec: http://i.imgur.com/fpaqO.jpg
6. Talents: http://i.imgur.com/xzw29.jpg
7. Glyphs: http://i.imgur.com/u5zZT.jpg
Here are my theories.
1. The character sheet is bugged, and my hit chance is actually at cap.
2. The system for normalizing item levels is bugged.
3. I'm overlooking something, or there is something going on that I do not know about.
Some extra info that might be relevant.
I am an Elemental Shaman, so I get Hit from my Spirit.
I have no "Hit" on my gear. I only have Spirit.
My professions are Engineering and Blacksmithing.
My helm is Energized Retinal Armor (Engineering Mail Intellect).
Meta Gem: Burning Primal Diamond (216 Intellect, 3% Increased Critical Effect)
Cogwheel Gems: 1 Sparkling Tinker's Gear (600 Spirit), 1 Quick Timker's Gear (600 Haste)
I have 1 Purified Roguestone (60 Int 120 Spirit), 4 Brilliant Pandarian Garnet (120 Int), and 1 Sparkling Lapis Lazuli (240 Spirit).
I'm not going to list all of my enchants, but I do have several, and some have Spirit in them.
EDIT: I have posted in the Bug Report forum, and will attempt to troubleshoot the problem. The thread I posted in is located here: http://us.battle.net/wow/en/forum/topic/6794350092?page=1#1
I am sorry for not checking there first.
EDIT2: Seems to be a bug with stat reductions on items with a higher item level than 463, and might have something to do with the stat being there because of a reforge.