Panels are different sizes when converting ggplot plot with facets

When converting a ggplot plot with facets to a plotly object the panels are different sizes. Margins are not subtracted from top and bottom rows so these panels end up being taller. This makes it hard to compare among panels. Margins for top and bottom of panels are equal so longer x-axis labels result in large margins on tops of panels with large spacing between panels and a low data-ink ratio.

library(dplyr)
library(ggplot2)
library(plotly)
library(reshape2)

p <- ggplot(data = tips,
            aes(x = sex, y = total_bill)) +
  geom_jitter(width = 0.1, height = 0) +
  facet_wrap(day ~ time, scales = "free_x", ncol = 2) +
  theme(axis.text.x = element_text(angle = 45),
        strip.text.x = element_text(size = 8, 
                                    margin = margin(t = 1, r = 0, b = 1, l = 0, unit = "pt")))

q <- ggplotly(p) %>% 
  plotly::layout(margin = list(l = 80, r = 0, t = 100, b = 100, pad = 0))

d <- rbind(q$x$layout$yaxis4$domain, q$x$layout$yaxis3$domain, q$x$layout$yaxis2$domain, q$x$layout$yaxis$domain)
df <- data_frame(lb = d[,1], ub = d[,2]) %>% 
  mutate(range = ub - lb,
         panelSpacing = lb - lag(ub))

Reproduce the issue with the supplied ggplotly() example and inspect the y-axis domain values collected in d. Start by tracing how facet panels and layout margins are converted, then verify that the top and bottom panels have equal sizes and that spacing reflects the configured margins.