Regardless of whether it is an Adwaita icon theme bug (I just tried with other icon themes and apart from the Adwaita one, all work well), I think if the patch is as simple as you propose (possibly covering more instances), we should do it - otherwise we might get flooded with bug reports regarding this problem and we might have to make a new release because of it anyway.
In fact, `gtk_image_new_from_stock()` is deprecated and we should migrate to `gtk_image_new_from_icon_name()` anyway so we can even call it a small step in the right direction.