Unclear if intended or not: Enemy movement causing interrupted spell

[X89K1]

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Date & Time: 01:00 - 02:00 UTC on Tuesday, 30 July 2019.
Frequency: Inconsistent
World name: Zalera
Character name: Hikari Nakajima
Retainer name: None
NPC name: None
Monster name: Eden Prime (Test works on any enemy that can make quick movements by itself.)
Class/Level: Black Mage, Level 80
Party or solo: Full Party
In-game time: 00:00 - 01:00
Area and coordinates: Eden's Gate: Resurrection (Savage)
Steps:
1. Fight Eden Prime up to the point it performs a dash to a corner. Auto face target should be turned on for the next step.
2. Cast a damaging spell before the boss's next dash WHILE being to the side of the boss or in the path the boss is going to dash through.
3. The spell has a random chance of finishing or being interrupted when the boss dashes past the caster. This is regardless of whether or not the cast is within slidecast range of finishing.

As the title says, I'm mostly just trying to see if the behaviour is intended.