i've always wondered about the term "short" when applied to baking and found this explanation...
"short,” in a baking context, means that there is a high proportion of fat to flour.This is usually just applied to non-yeast doughs. Usually these short doughs are very rich, crumbly, and tender with butter. They tend to be crisp instead of chewy, and slightly sandy. Shortbread is the quintessential “short” dough – it’s even in the name! You do want to make sure that the flour is very well-incorporated into a thick, rich dough like this.
i believe the last line is very key to the success of good shortbread. mixing this dough is generally a struggle toward the end as aside from the butter, all other ingredients are dry. i've literally broken wooden spoons while mixing the dough, though i don't use them anymore. from the previous comment, i've got to think the texture of the shortbread will be different with the inclusion of the rice flour. hopefully not as the most disastrous time i tried substituting margarine for butter some years ago ... it was horrible.