hovermode='x unified' is causing unexpected behavior together with group_by()

library(tidyverse)
library(plotly)

TexasCities_plus_Houston <- ggplot2::txhousing %>% 
  group_by(city) %>%
  plot_ly(x = ~date, y = ~median) %>%
  add_lines(
    name = "Texan Cities", 
    text = ~paste0(city, "\n", median),
    hoverinfo = "text+x"
  ) %>%
  filter(city == "Houston") %>%
  add_lines(name = "Houston")

This works as expected (but the limitation is that it is hard to find Houston city to hover on):
TexasCities_plus_Houston %>% layout(hovermode = "closest")

This solves the above limitation, however, it does not matter which point you hover on, the same city name is shown ("Wichita Falls"). The "median" variable changes as expected, the problem seems to be solely with the variable used in group_by(), in this case, "city".
TexasCities_plus_Houston %>% layout(hovermode = "x unified")

Iniziate eseguendo il riproduttore R fornito con plot_ly(), group_by(city), add_lines() e layout(hovermode = "x unified"). Confrontate le etichette di hover unificate con hovermode = "closest" e tracciate il modo in cui viene selezionato il valore city raggruppato; il lavoro è concluso quando l'hover unificato mostra la city appartenente al punto su cui si è posizionato il cursore, preservando al contempo la mediana variabile.