The reason crit is shown twice is because once you get to the shatter cap, crit drops well under mastery in value.
Raid bosses have a mechanic that reduces your crit chance on them by 3%. This 3% is applied to your base crit so:
(28-3) x 2 + 50 = 100%
You shouldn't have to worry about the shatter cap for a while due to gear levels and haste being worth more.
It isn't calculated that way, though. It adjusts your modified crit chance rather than your base crit chance.
This is the formula: ( Base Crit * 2 ) + 50 - 3 = Shatter Crit chance
(26.5*2) + 50 - 3 = 100%
So 26.5% base crit is your soft cap.