Why is ggplot scale_manual not correctly rendered in ggplotly?

I am using ggplot scale_manual to extend legend items to include values absent in the data and it works. However, when I use ggploty to render it, it doesn't work. Is there a work around this?

lims <- c("4", "6", "8", "10")
cols <- c("4" = "blue", "6" = "darkgreen", "8" = "red", "10" = "orange")
labs <- c("4" = "four", "6" = "six", "8" = "eight", "10" = "ten")

p <- ggplot(mtcars, aes(mpg, wt)) +
  geom_point(aes(color = factor(cyl)))

q <- p + 
  scale_color_manual(name = "Cylinder", values = cols, labels = labs, limits = lims)

# This extends the legend items by including "ten".
q

# In this case, the added legend item "ten" is dropped.
ggplotly(q)

Haven't found an option to prevent the unused category from being dropped. But one way to achieve your desired result would be to use a invisible geom_point layer which maps the unused category on color and NA on x and/or y:

library(plotly)

p <- ggplot(mtcars, aes(mpg, wt)) +
  geom_point(
    aes(color = factor(cyl))
  ) +
  geom_point(
    data = data.frame(x = NA_real_, y = NA_real_),
    aes(x = x, y = y, color = factor(10))
  ) +
  scale_color_manual(
    name = "Cylinder",
    values = cols,
    labels = labs,
    limits = lims
  )

ggplotly()