Unity drawing particles incorrectly

Hi! I was having a slight issue with the particle drawing yesterday, for some reason it seems to be 'filling in' empty pixels on my particle sprite. For example, here's the sprite itself, a very simple 3x3 pattern:

Particle

And here's what's being drawn:

Drawn Screenshot

A quick check in paint,net shows that the corner squares in the sprite file are indeed empty. I'm using the Alpha Blended - Premultiplied shader, is it simply not designed for ultra-tiny sprites? Any info would be appreciated!