Fractal bug: Sugar Rush in 99CM causes the Siax encounter's mechanics to speed up

Normally, during the split phase of Siax when the four Echoes are channeling Caustic Explosion, the detonations occurs simultaneously with Siax's own channel.

With the Sugar Rush instability, this changes - but only on the 33% phase. The 66% phase operates normally, but on the 33% phase, Sugar Rush causes the four Echoes to detonate 35% earlier than Siax's actual timer.

The Echoes' explosion animation can be seen completing well before the mechanic reaches the edge of the room.

Is this intended? It sort of makes sense as it's a channeled attack and they are veterans, thus qualifying Caustic Explosion for Sugar Rush's speed, but it (a) directly affects a specific mechanic of this specific boss, turning Sugar Rush into a CM for the CM, and (b) does not occur on the 66% phase despite the Echoes being the same in both. Something just isn't right with this instability on this encounter.

Edit: Further VOD review has me even more confused. We spent two hours trying 99CM with Sugar Rush tonight and cleared the 66% phase easily yet the 33% phase wiped us due to faster detonation - but one wipe at 66% also featured an earlier detonation. I don't see a consistent application of this.