event_data("plotly_relayout") always fires NULL

[cpsievert]

library(shiny)
library(plotly)

ui <- fluidPage(
  plotlyOutput("plot")
)

server <- function(input, output, session) {
  
  output$plot <- renderPlotly({
    plot_ly(x = 1)
  })
  
  observe({
    print(event_data("plotly_relayout"))
  })
  
}

shinyApp(ui, server)