Can't override dynamically created method

Question

Reproducible example:

Parent <- R6::R6Class(
  "Parent",
  lock_objects = FALSE,
  public = list(
    initialize = function() {
      # I wan't to create many methods dynamically in the loop.
      self[["foo"]] <- function() {
        print('foo')
      }
    }
  )
)

Child <- R6::R6Class(
  "Child",
  inherit = Parent,
  lock_objects = FALSE,
  public = list(
    foo = function() {
      super$foo()
    }
  )
)

child <- Child$new()

Error:

Error in self$foo <- function() { : 
  cannot change value of locked binding for 'foo'

Why I'm getting this error when in both Parent and Child lock_objects = FALSE?