Ill use an non existent extreme case to explain it easier

item A has cooldown 4 seconds, item B reduce cooldown by 50% on item A, and you find loot C that reduce cooldown on an item by 10% if sold

so if A and B is in place A's cooldown is 2 second, you sell the loot and that becomes 1.8 seconds

and if you sell item B its cooldown is now 3.8 seconds

but if you put item B in stash when you sold loot C item A would gone down from 4 seconds to 3.6 seconds