I already have a very rare purple Energy Weapon doff that has a 50% chance of reducing any beam special attack recharge by 10 seconds. After spending 19.3 million EC credit on the exchange to get a 2nd one, thinking that 50%+50% = 100% chance of reducing the recharge by 10 seconds. Well, think again, they don't stack. The probability is still at 50%.
Someone please tell me this is a bug that needs to be fixed or let this serve as a warning to others so that they don't make the same mistake as I did.