Jon A. Cruz wrote:
The "legacy icons" are actually special cases where there is a
name used by themes that does not match the older name used
internally by Inkscape.
I am 100% sure those are the only icons looked up in the theme, because I
tested it.
Looking at my current OS X config, I see eleven of the twenty-five I
see on my main toolbar are ones that come from my local theme.
You are probably confusing GTK stock item theming with application theming.
Inkscape uses some icons from the current theme because it uses GTK stock
items. The icons used for e.g. the tool switcher ar not themed.