subplot - merging titles following ggplotly conversion

data(faithful)

p1 <- plotly::ggplotly(
  ggplot(faithful, aes(x = eruptions)) + 
    geom_histogram(bins = 20) + 
    theme_minimal()  + 
    labs(title = "A.")
)

p2 <- plotly::ggplotly(
  ggplot(faithful, aes(x = waiting)) + 
    geom_histogram(bins = 20) + 
    theme_minimal()  + 
    labs(title = "B.")
)

pl <- subplot(p1, p2, nrows = 1, titleX = TRUE)

## note  that changing to labs(tag = "A.") results in loss of the 'tag' at the ggplotly function.  

I am creating a gglot (histogram, in this case) which includes a sub-panel label. I want to then convert to a plotly figure using the plotly::ggplotly function. The label is transmitted faithfully to each of p1 and p2. However, when combining these into a subplot, the label seems to be merged . I lose the 'A.' label on the first plot p1, generally. The titleX option does not prevent this from occurring.

先从使用 ggplotly 和 subplot 的可复现 faithful 数据示例开始，然后跟踪在启用 titleX 时 subplot 如何组合 p1 和 p2 的标题。确认 labs(title = "A.") 和 labs(title = "B.") 的行为；转换和组合后两个标签仍保持可见即表示完成。