I'm not quite sure whether this a bug or not however this is the issue:

When you fill a region of blocks with fill, I assume it goes through block by block and processes each one individually, which makes sense. However, before the entire process of the fill has been completed, the game seems to schedule the update of blocks around the one that has been changed, which again makes sense. However, an issue occurs when it schedules an update in a block which is being filled.

Example:

If a setup like this is achieved (through commands), and then all of the grass is set to air all at once with a fill command, the centre grass will make a sound and generate particles. I assume this is because one of the 4 neighbouring grass blocks has been broken sequentially by the fill command and has updated the centre grass before it has actually been processed by the fill.

If the grass surrounding the centre grass is removed, leaving the centre grass and then doing the fill, there is no particles and no sound as you should expect.