This is pretty harmless issue, except it's triggering my CSS Lint errors for no obvious reason.

Apparently, if I use gallery(# of #), first child of the class where mixin is applied has duplicate declaration.

This is example code that I've found on codepen while looking for solution, it has the same issue as I'm describing. Inspect first element in row on both of the rows, it has same duplication problem.

This is the code generated on first element in row:

  margin-left: 0;
  margin-right: -100%;
  clear: both;
  margin-left: 0;

I guess this can be tagged as an improvement. In meantime, I'll be looking at some post-css script to remove duplication, because CSS Lint is giving me troubles because of this.