There are two types of crit chance bonus - capped and uncapped. To get your actual (character sheet) crit chance, you add up the capped bonuses. If the total capped is above 50%, you reduce it to 50% (this is the cap). Then add all the uncapped bonuses. With sufficient uncapped bonuses, you can get to 100% crit chance, but the capped bonuses cannot exceed 50%.

The "+X% crit chance per Enraged token" is a capped bonus. It will boost you up to 50% and no further. "Revenge" from the Critical Hits passive tree ("+1% crit chance on attack, stacks until a critical hit") is an uncapped bonus and will keep stacking up to 100% crit chance. Additionally, Revenge currently seems to apply +2% per stack (perhaps a bug or tooltip mistake). With a high-crit build, you probably have Revenge unlocked.

Now, when you look at your crit chance during a mission with 10 stacks of Enraged, your capped bonuses likely exceed the cap. Let's say your enchant is +3% crit chance per enraged and you have +40% of other capped bonuses from your gear. Your capped total is +70%, reduced to +50% by the cap. Let's also say your last two shots did not crit, so you have 2 stacks of Revenge, for +4% uncapped bonuses, a total of 54% actual crit chance. 

In order to lose an Enraged token, you fire a shot into a wall (I assume this is how you are testing). Your capped total reduces to +67% but is still limited to the same +50% by the cap. You fired a shot that did not crit, so gained a Revenge stack. Your uncapped bonuses are now +6%. Your actual crit chance is now 56%. You lost an Enraged token, but your actual crit chance increased due to the interaction with the cap and Revenge's uncapped nature. This will continue until your capped total drops below 50%.

If you keep firing into a wall, Revenge will continue stacking until you get to 100% actual crit chance. Remember, though, that all stacks are lost on the next crit, so it doesn't make that huge a difference in practice.