The problem lies in the coding of the skill. ANet seems to not even realize an easy “half-fix” for this problem.
Well, to explain:
If it would stack swiftness (as it did in beta), mesmers would set it on the ground and run through it five times (or so) during its duration getting the swiftness stack each time.
The Swiftness Symbol of the guardian is similar, yet better. It ticks every two seconds and grants you 8s of swiftness if you’re inside it. When you enter it without any swiftness, each tick resets the swiftness to 8s. If you have any other source of swiftness, it doesn’t do anything but reset the white border of the previous swiftness.
But you can’t change the curtain to the slightly better behaviour since it’s based on time ticking.
A very simple “half-fix” for this problem – without reenabling the super stacking from the beta – would be to make it not stacking (as it does not right now), but replacing if the current swiftness it shorter than the new one. So running through a 11s curtain with 5s swiftness left, setting it to 11s (instead of 16s) and running through it with 20s swiftness left, leaving it at 20s.
A “full fix” of any ground targeted, duration based, swiftness granting skill would require advanced coding with more memory and more checkups.
