我可以让ggplot在轴标签和图例中打印日文Unicode字符，但不能在标签中打印。这是一个错误吗？
library(extrafont)
library(ggplot2)
data_frame <- cbind.data.frame("number"=c(1:3), "kana"=c("い","ろ","は"))
ggplot(data=data_frame, aes(kana, number)) +
geom_point() + theme_gray(base_family = "Meiryo") ##works great
ggplot(data=data_frame, aes(kana, number, label=kana)) +
geom_point() + geom_label() + theme_gray(base_family = "Meiryo") ##no such luck