Sankey labels appear at strange locations

In vertical sankeys, mouseover labels of flows appear at strange locations, some of them outside the drawing area.

See here:

library(plotly)
library(rjson)

json_file <- "https://raw.githubusercontent.com/plotly/plotly.js/master/test/image/mocks/sankey_energy.json"
json_data <- fromJSON(paste(readLines(json_file), collapse=""))

p <- plot_ly(
  type = "sankey",
  domain = list(
    x =  c(0,1),
    y =  c(0,1)
  ),
  orientation = "v", # this is the only change to the original example
  valueformat = ".0f",
  valuesuffix = "TWh",
  
  node = list(
    label = json_data$data[[1]]$node$label,
    color = json_data$data[[1]]$node$color,
    pad = 15,
    thickness = 15,
    line = list(
      color = "black",
      width = 0.5
    )
  ),
  
  link = list(
    source = json_data$data[[1]]$link$source,
    target = json_data$data[[1]]$link$target,
    value =  json_data$data[[1]]$link$value,
    label =  json_data$data[[1]]$link$label
  )
) %>% 
  layout(
    title = "Energy forecast for 2050<br>Source: Department of Energy & Climate Change, Tom Counsell via <a href='https://bost.ocks.org/mike/sankey/'>Mike Bostock</a>",
    font = list(
      size = 10
    ),
    xaxis = list(showgrid = F, zeroline = F),
    yaxis = list(showgrid = F, zeroline = F)
  )

Result:

This is the mouseover of the flow currently shaded in dark grey. In general, labels of flows to the left of the plot appear at rather correct locations and labels of flows to the right of the plot are off or do not display at all.

> version
               _                           
platform       x86_64-w64-mingw32          
arch           x86_64                      
os             mingw32                     
system         x86_64, mingw32             
status                                     
major          3                           
minor          6.1                         
year           2019                        
month          07                          
day            05                          
svn rev        76782                       
language       R                           
version.string R version 3.6.1 (2019-07-05)
nickname       Action of the Toes      

> packageVersion("plotly")
[1] ‘4.9.1’

Start by running the supplied R plot_ly Sankey example with vertical orientation and compare hover labels across the drawing area. Trace the Sankey flow hover-label positioning entry point and verify that labels remain aligned with their flows, including links on the right; add or run a regression check if the relevant test location is found.