To replicate: run command /summon minecraft:area_effect_cloud ~ ~ ~ {Radius:0}
Observe black and white particles appearing briefly, then they stop even though the cloud is still present (visible with hitboxes shown). Expected behavior is for no particles to appear as in previous versions.
Observed starting in snapshot 25w09a (likely relevant: this is when the behavior for Duration:-1 was added), not in 25w08a or sooner, and up until the current release candidate.
I’ve just realized that the
WaitTimedata is now defaulting to 20 ticks instead of 0, which is the cause. When summoning withWaitTime:0the old behavior is observed. However, as this change was not explicitly documented (at least not anywhere I saw), I would still consider this a bug.