Suppose a BlockExplodeEvent was handled by an event handler. If the handler sets the event to cancelled, it will only be partially cancelled.

Attributes of the explosion that have been seen to be cancelled:

• Block breaking

Attributes of the explosion that have not appeared to be cancelled:

• The explosion sound
• The damaging of nearby entities

I created a simple plugin to recreate this issue: https://github.com/Perzan/BlockExplodeEvent-Glitch

The command is "/GenerateCancelledExplosion" or "/GCE"

PS:

If you want to adjust the power of the explosion, use "/GCE <Power Integer>"