When leveling up Dragon Tail while a projectile already flies from a previous cast, that cast will apply the new level's damage and stun duration, instead of the damage and stun duration of the level it was cast on.

The same goes for talent bonuses. You can level up the +1.25s stun duration talent and it will instantly apply to the current projectile.

Repro:
1. Cast Dragon Tail on level 1 in Elder Dragon Form
2. While the projectile travels, level it up to 2

Result: The projectile will now use the level 2 damage and stun duration on the target, even though you originally cast it on level 1.

Expected: The damage value and stun value (including the talent bonus) should be set upon cast, and be based on the set variable, and not check level on impact.