Stackgroup with scatter and more than 1 axis not working properly?

I am doing a scatter plot with stackgroups. I would like to use the x2 and y2 axises. When I use the regular x and y axis, the result is correct. The data frame below is used. The first Plotly chunk is for the regular x and y axis behavior. The second one tries to use x2 and y2 but only the 2nd stack group is shown. I think this might be a bug.

library(datasets)

df <- mtcars[1:5,]
df$mpg <- 0
df$qsec <- df$qsec + runif(length(df$qsec),min=-3, max=5)
df$hp <- df$hp + runif(length(df$hp),min=-30, max=30)
df$names <- rownames(df)
rownames(df) <- NULL

df2 <-  mtcars[1:5,]
df2$names <- rownames(df2)
rownames(df2) <- NULL

df<- rbind(df,df2)

Below works but since the y axis range is quite different for qsec and hp, a second y axis is needed.

library(dplyr)
library(plotly)

plot_ly(type = "scatter",mode='none', width = 800, height=420) %>%
          add_trace(
                  mode = "lines",
                  stackgroup = "red",
                  orientation = "h",
                  x = df$mpg,
                  y = df$qsec,
                  line = list(color = "red"),
                  name = df$names) %>%
add_trace(
                  mode = "lines",
                  stackgroup = "blue",
                  orientation = "h",
                  x = df$mpg,
                  y = df$hp,
                  line = list(color = "blue"),
                  name = df$names)%>%
          layout(  xaxis =list(title="mpg", side = "bottom"),
                   yaxis =list(title="qsec",side = "left"))

Here, the following is tried.

library(dplyr)
library(plotly)

plot_ly(type = "scatter",mode='none', width = 800, height=420) %>%
          add_trace(
                  mode = "lines",
                  stackgroup = "red",
                  orientation = "h",
                  x = df$mpg,
                  y = df$qsec,
                  line = list(color = "red"),
                  name = df$names) %>%
add_trace(
                  mode = "lines",
                  stackgroup = "blue",
                  orientation = "h",
                  xaxis = "x2",
                  yaxis = "y2",
                  x = df$mpg,
                  y = df$hp,
                  line = list(color = "blue"),
                  name = df$names)%>%
          layout(  xaxis =list(title="mpg", side = "bottom"),
                   yaxis =list(title="qsec",side = "left")
                  ,yaxis2 = list(title = "hp", side = "right", overlaying = "y")
                  ,xaxis2 = list(title = "mpg", side = "top", overlaying = "y")
                  )  

I also tried using fill = "tozerox" and fill = "tozeroy" instead of orientation="h"|"v" but this doesn't work at all. Thank you in advance for taking a look. :-)

Start by running the two supplied R examples and compare the output when the second trace uses xaxis = "x2" and yaxis = "y2" with stackgroup. Trace how add_trace and layout handle stacked scatter traces across multiple axes; the issue is done when both stack groups render correctly with the secondary axes, or the supported limitation is documented.