Energy Weapon DOFF ability do not stack
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. 
it stacks but it doesnt stack in that way...it pretty much adds another 50% chance to proc....to you could have it proc twice, once, or not all. i myself am running 2 blue beam boffs and thats how it works.

As cynder wrote, it does not stack the proc chances, but chains it. So with two doffs you have a 75% chance that at least one of both will proc. If you use 3 doffs you increase this chance to 88% and to 50% that two will proc.
Its the way all doff procs work, not just that for the energy weapon doffs. 
Thank you both for your comments. I get it now. My mistake in understanding the way probability is calculated in this game. As I tested it more, it did increase the proc rate to about 75% or even a little higher, like 10/12. So the doff is having an impact for sure. And sometimes both doff will proc and reduce the recharge time by 15 seconds since that's the maximum they can reduce till global cooldown.

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At least security escort doffs don't stack that way. It seems they either all proc (and with 3 purples, spawn an army of 8 redshirts :D) or none of them do (so I get the standard 2). For most doffs, the effect is not quite as visible so I couldn't say if other stackable doffs stack like that, but they could. 
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