Breaking a Poise Cluster with Shears plays the Poise Cluster break sound twice.

Hitting a Poise Cluster entity a third time and causing it to drop as an item does not play any sound.

This last "issue" could be considered more of a suggestion:
Poise Cluster blocks that have another block above them can be destroyed without them turning into a Poise Cluster entity, but they do not drop anything when destroyed this way without Shears. This is inconsistent with Poise Cluster entities, which drop as items no matter what item they are hit with. For consistency, Poise Cluster blocks could be changed to always drop when destroyed. Shears would still be useful for collecting Poise Clusters quickly without them floating upwards.