kohske/ggplot2 — comment on commit 1815bf1b79ba8c4559587f8d7aca84ae6335af2f
File:  line 0
By hadley:

I'm not sure why this is needed - the calculate function already takes care of the grouping, and then the extra vars should get added back on. Since I don't think `stat_sum` has changed lately, I wonder if the bug is coming from somewhere else.