geom_line() with text mapping and without group mapping doesn't render

I have a base-barchart plot with working tooltips.

I want to add a line-chart by clicking a radioButton on top of the barchart, also with hovering tooltips, which is not working as I expected.

1. When adding a text argument to the additional line, the line is not showing up, but when I hover over the pot, the labels of the line show.
2. When uncommenting the text argument (line 28), the line shows, but no hovering tooltips, as expected.
3. When removing the tooltip = "text" from the ggplotly call (line 33), the line and the tooltips shows up, but the formatting is not like I want it to be.

library(shiny)
library(ggplot2)
library(plotly)

dfN <- data.frame(
  time_stamp = seq.Date(as.Date("2018-04-01"), as.Date("2018-07-30"), 1),
  val = runif(121, 100,1000),
  col = "green", stringsAsFactors = F
)

ui <- fluidPage(
  br(),br(),
  checkboxInput("zus1", value = FALSE, label = HTML("add Line")),
  plotlyOutput("plt")
)

server <- function(input, output, session) {
  output$plt <- renderPlotly({
    key <- highlight_key(dfN)
    p <- ggplot() +
      geom_col(data = key, aes(x = plotly:::to_milliseconds(time_stamp), y = val, fill=I(col),
                               text=paste("Datum: ", time_stamp, "<br>")))
    
    
    if (input$zus1 == TRUE) {
      p <- p + geom_line(data = dfN, aes(x = plotly:::to_milliseconds(dfN$time_stamp), y = val
                                         ## This text is not showing up, but hovering shows the labels
                                         # , text=paste("Value: ", val)
                                         ), color="red")
    }
    
    ## Removing tooltip = "text" shows the additional line and hover-labels but with horrible formatting.
    ggplotly(p, source = "Src") %>% 
      highlight(selectize=F, on="plotly_click", off = "plotly_doubleclick", color = "blue") %>% 
      layout(xaxis = list(tickval = NULL, ticktext = NULL, type = "date"))
  })
}

shinyApp(ui, server)

Start with the supplied Shiny example, focusing on the geom_line text mapping and the ggplotly(p) call with tooltip="text". Reproduce the case where the line is hidden but its labels appear, then determine what behavior makes the line and correctly formatted hover tooltips render together.