Stacked stat bonus creates a new bonus where probability/percent of bonus exceeds the limit or 100%, but is applied at reduced rate.
Example: suppose a player has 250% chance to do a Critical Strike(defined for simplicity as attack that deals x2 of max damage and bypasses chance-to-hit).
Since he already has 100%+ chance to Critical Strike, it always does x2 damage, but since there is extra 150% bonus it converts(usually at x/2) to 75% to do another Critical Strike on top of that dealing x4 damage(further chance appear where there is more that 100% for second,third,fourth critical strike).

Example2:Resistances above the resistance cap(usually 99%/95%) creates secondary resistance check(applied again to the damage: e..g. 105% resist with 95% cap, create 95% resists =5% of damage than 10%(105-95) resistance applies, leaving 4.5% damage).

Example3: 400% chance to cast Fireball at attacker when struck, will adjust the Fireball damage by (400-100)=+300%(instead of x4 fireballs which wastes graphics space).

This allows benefits for stacking the modifiers beyond the limits, and should be balanced accordingly(adjusting the secondary modifier to work at 1/2 or 1/4 the strength of original).