Guild Wars 2

When any player uses swiftness on you
and when it’s about to run out, cast a symbol of swiftness which in my case should give 15 seconds of swiftness. It however will only update the swiftness duration to 4 or 5 seconds instead of giving the full 15 seconds of swiftness.

so that means when multiple ppl with low duration swiftness run through my field it will only give them 4 or 5 seconds of swiftness instead of the full 15 seconds.

Actually, it gives them + 1s swiftness duration if you already have swiftness. + 1s because it pulses each second. So if you don’t have swiftness it goes 0s -> 8s --> 7s -> 8s --> 7s -> 8s … If it’d give + 8s every pulse, it’d be
0s -> 8s --> 7s -> 15s --> 14s -> 22s --> 21s -> 29s --> 28s -> 36s Swiftness.
And that’s simply why it only gives you one additional second when you already have swiftness. With 30% boon duration, it’d become 48s swiftness duration with a 15s CD.

Be happy that it actually grants you one additional second, temporal curtain voids if you have any swiftness on you.

It’s not a bug, but a patchfix.

Nretep.2564:

Actually, it gives them + 1s swiftness duration if you already have swiftness. + 1s because it pulses each second. So if you don’t have swiftness it goes 0s -> 8s --> 7s -> 8s --> 7s -> 8s … If it’d give + 8s every pulse, it’d be
0s -> 8s --> 7s -> 15s --> 14s -> 22s --> 21s -> 29s --> 28s -> 36s Swiftness.
And that’s simply why it only gives you one additional second when you already have swiftness. With 30% boon duration, it’d become 48s swiftness duration with a 15s CD.

Be happy that it actually grants you one additional second, temporal curtain voids if you have any swiftness on you.

It’s not a bug, but a patchfix.

It’s a bug. Only your first sentence was correct. You’re describing the way it should work, but that’s not what happens.

If you already have, say, 4 seconds of swiftness, it goes more like:
4s —> 5s --> 4s —> 5s --> 4s —> 5s --> 4s —> 5s --> 4s —> 5s --> 4s —> 3s --> 2s —> 1s --> 0s

Using your numbers above, we would expect it to be more like:
4s —> 12s --> 11s —> 12s --> 11s —> […]

I’ve posted a more thorough explanation, including screenshots, here.