Tooltip showing "NA" when facets variable has level with one obs

Tooltip shows "NA" instead of value when using facet_wrap/facet_grid with a categorical variable that has one level with only one observation. The tooltip for the level that has only one observation appears correct. But the tooltip for all other facets shows "NA". This issue occurs only when at least one of the levels of a categorical variable used in facet_wrap has exactly one observation. With two observations per level, the problem disappears.

library(plotly)

d <- data.frame(matrix(nrow = 100, ncol =0))

d$cat1 <- sample(LETTERS[1:4], 100, replace = TRUE, prob = c(0.1, 0.2, 0.65, 0.05))
d$x <- rnorm(100)

ggplotly(
  ggplot(data = d, aes(x = x)) +
    geom_histogram() +
    facet_wrap(cat1 ~ .)
)

使用 ggplotly 和 facet_wrap 运行提供的 R 重现程序，其中包含一个只含一条观测值的分类水平。跟踪工具提示值如何跨分面进行分配，然后验证该 singleton 水平和所有其他分面是否显示其预期值，而不是 "NA"。