Endurance Charge duration not working with Spectres?

I have a Perfect Warlord spectre to grant me endurance charges. The default 10 second duration is just short enough that it occasionally falls off, so I specced one duration node. It's still 10 seconds. Is this a bug, or does it just not work with this particular spectre?

I do indeed believe that these endurance charges are not affected by your increased charge duration. Out of battle you should also be able to keep the charges up. But once the specter enters battle he might use attacks and movement skills and won’t use enduring cry on time. So expect a small downtime.

I would suggest getting 2x 20% charge duration and then gain the eater/ exarch( not sure which one) to gain an endurance charge every 13 seconds. The specter slot you could use for a perfect turtle then for example (determination aura)