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 el problema con el ejemplo de ggplotly() proporcionado e inspecciona los valores del dominio del eje y recopilados en d. Empieza siguiendo cómo se convierten los paneles facet y los márgenes del layout; después, verifica que los paneles superior e inferior tengan el mismo tamaño y que el espaciado refleje los márgenes configurados.