Armor description states :

Ignore a single incoming hit every 10 seconds. As long as you haven't taken damage in the last 10 seconds, your gadget energy recharge rate is increased significantly.

 

However, there is absolutely no change in gadget regen rate with this armor equipped. The effect where you ignore a single hit every 10 seconds is working correctly but the energy regen does not. I tested this both in and out of combat by spending energy and watching it regen, even tested taking a hit then waiting over 20 seconds without taking a hit just to be sure, still zero change in regen rate.

So after further testing I retract the bug report. It does seem to improve regen but by a small amount that it's not very noticable and is suceptible to heavy diminishing returns when paired with a helmet that adds energy regen as well. Also, combat energy regen reduction is EXTREMLY severe. I would not really consider the wording of "significantly increased" to be especially valid on this item.

It seems to add roughly a 30-40% energy regen increase. When using a 160% regen helm, this bonus goes down to around a 10% increase when diminishing returns kick in.

My Results measuring the time it took to regen 1 energy bar :

1 gadget bar = 50 energy

 

Outside combat

WITHOUT any armor equipped : ~6.25/second (8.4 seconds to fill 1 bar)

WITH the Mathematician Mantle equipped : ~8.1/second (6.1 seconds to fill 1 bar)

WITH a 160% energy regen helmet : 16.6/second (3 seconds to fill 1 bar)

WITH a 160% energy regen helmet + Mathematician Mantle : 18.5/second (2.7 seconds to fill 1 bar)

 

In combat

WITHOUT any armor equipped : 1/second (50 seconds to fill 1 bar)

WITH the Mathematician Mantle equipped : 1.42/second (35 seconds to fill 1 bar)

WITH a 160% energy regen helmet : 2.63/sec (19 seconds to fill 1 bar)

WITH a 160% energy regen helmet + Mathematician Mantle : 2.9/sec (17.3 seconds to fill 1 bar)