viral bluff
When the target location for an Arrow Shower cast happens to be on sloped terrain, it will orient the AOE's circle to be tangent to the slope at the centerpoint of the circle. This causes the skill's visual effect's location to be desynced from the target circle, and this desync is exaggerated based on how extreme the terrain's slope is.
Good spot to test this is the hilly terrain on the Fairy Glen map.
viral bluff
Just realized, this can also be done on flat ground, and with additional skills beyond just Arrow Shower (Slow Trap, etc.), if a specific method is used.
Have the character facing a certain direction, and simply aim the cursor directly behind the character before casting the skill. If it's close enough to the character, the AOE circle will be rotated into the ground plane, desyncing the skill's visual effect if it has one.