Shiny, checkboxInput and observeEvent

Given this small shiny app:

library(shiny)
library(tidyverse)
library(shinydashboard)

ui = dashboardPage(
  dashboardHeader(),
  dashboardSidebar(),
  dashboardBody(uiOutput("graphs_ui")),
)

server <- function(input, output, session) {

  popup <- function(){ modalDialog(easyClose = T,'popup window triggered')}

  output$graphs_ui <- renderUI({
    map(1:2, ~{
      tagList(box(title = paste0("Isolation: ", .x),

                  status = "info",
                  footer = checkboxInput(paste0("check_", .x),"")))})
  })

  observeEvent(map(grep(pattern = "check_", names(input), value = TRUE), ~input[[.]]),{
    showModal(popup())}, ignoreInit = T)
}

shinyApp(ui, server)  

I want to trigger a dialog "popup" upon checking one of the checkboxes. Problem is that the dialog already pops up after initalizing the app, althoug I set ignoreInit = TRUE. I have no idea why, since the behavior remains when using actionButton.