This bug has been around for about since 1.2 came out: When a large number of particles are in the world, from various causes (picture example is dragon's breath), many of the particles will be oversized to varying degrees. This primarily occurs with the ender acid, but can even be caused by things as mundane as fireworks, or, rarely, breaking blocks.

Side note: this causes an immense framerate drop, which leads to me not being able to fight the Ender Dragon. May be a device issue, though.

Also, this is technically a dupe of MCPE-30978, though I believe the writer was unaware of what was actually happening.