I'm guessing this doesn't happen often right? The only time I can think of this happening is when you are slightly out of sync with the server due to latency. If Soul Blade: Assemble ends you shouldn't even be able to use the skill at the increased range - your character should start running forward until it's in range to use the skill - if there is a bit of latency then it might let you cast it at the increased range if Assemble has run out right at that split-second, but when the server checks stuff and sees you are not in range it will stop the skill from landing on the target. There isn't really anything I can do about this scenario.

it happens quite often for me on soul blader.
it doesnt happen with any of my other char classes that have activation requirement skills.
ie: wiz adv ice infusion etc.. when using those skills if adv ice infusion isnt active the skill isnt usable and if you get the skill off before it deactivates then it still casts as expected.

with soul blader if you get the skill off and soul emsemble deactivates your range/reach drops immediately and the skill nerfs off and doesnt cast properly with range its like it turns into a normal melee attack instantly so if you are away from target you attack but with normal melee attack range not reach so it hits nothing(nerfs off).

im guessing its not latency since it doesnt happen with other classes i play that have activation requirement skills but then again most other classes only have one or two skills like this where as soul blader almost all of the skills differ depending on wether soul ensemble is active or not so perhaps it is more noticeable with this class due to the chance increase of soul ensemble running out whilst using them.
just seems off/buggy/choppy to me ..when it does happen i think to myself this cant be right can it just seems wierd and unfluid.
but im not avid sb guru so maybe its just normal for this class.