Thanks for the quick reply! I think I've done everything right, but I only get a new definition (loaded) when I use the write-to-dev-null trick (but it's painfully slow!). When I use the add_cpoint() or add_group() trick my SKP file is ignored and I get the same GUID back. Here's my full script, if you don't mind taking a look:

require "sketchup.rb"

module RefreshComponent
  def self.force_reload_component_definition!(model, definition)
    definition_path = definition.path
    definition_name = definition.name
    definition.name = definition.name + rand.to_s
##    definition.entities.add_cpoint(ORIGIN)     ## <== this causes GUIDs to match (fail)
    definition.save_as("/dev/null")              ## <== this causes new definition load (success)
    reloaded_definition = model.definitions.load(definition_path)
    puts "Old GUID; " + definition.guid
    puts "New GUID; " + reloaded_definition.guid
    reloaded_definition
  end

  def self.reconnect_component_instances!(model, old_definition, new_definition)
    model.start_operation("Remap instances")
    old_definition.instances.each { |instance| instance.definition = new_definition }
    model.commit_operation
  end

  def self.delete_component_definition!(model, definition)
    model.start_operation("Delete Definition")
    definition.entities.erase_entities(definition.entities.to_a)
    model.commit_operation
  end

  def self.refresh_component(model, definition)
    model.start_operation("Reload current component definition", true)
    reloaded_definition = force_reload_component_definition!(model, definition)
    reconnect_component_instances!(model, definition, reloaded_definition)
    delete_component_definition!(model, definition)
    model.commit_operation
  end

  def self.start
    model = Sketchup.active_model
    model.start_operation("Reload component definitions from file", true)
    model
      .selection
      .select { |entity| entity.is_a?(Sketchup;;ComponentInstance) }
      .map { |instance| instance.definition }
      .uniq
      .each { |definition| refresh_component(model, definition) }
    model.commit_operation
  end
end 

unless file_loaded?("refresh_component.rb")
    UI.add_context_menu_handler do |context_menu|
      context_menu.add_item("Reload Current Component Definition") {
        RefreshComponent.start
      }
    end
   file_loaded("refresh_component.rb")
end

This is a very useful thread: I'm trying to apply this workaround (add_cpoint) but I'm still getting an identical GUID. Would you mind posting the actual solution, so there's an explicit example I can refer to? For what it's worth, this is my attempt (I'm trying to automate re-loading certain components from their .skp files):

    model = Sketchup.active_model
    selection_set = model.selection
    selection = selection_set[0]
    definition = selection.definition
    definition.entities.add_cpoint(ORIGIN)   # not sure if I'm applying this to the correct entity
    new_definition = model.definitions.load(definition.path)
    puts "Old GUID; " + definition.guid
    puts "New GUID; " + new_definition.guid

I'm not sure if I'm applying add_cpoint() to the right entity; also I'm not sure whether creating an empty group is a better workaround as suggested in the thread, or how to do that!).

Finally, this is how I hope to replace the instances (based on someone else's example):

      definition.instances.each { |instance|
        instance.parent.entities.add_instance(new_definition, instance.transformation)
        instance.erase!
      }

Many thanks, and hugely appreciated!

Mike

I've verified that this bug was not present in Sketchup Free 7.1.6859 . I think it may have been introduced in Sketchup Free 8 (but haven't verified that). It's certainly been around for several years, surprisingly.

Mike

I've actually noticed this bug for several years: if I create a surface inside a group, then cut a hole in that surface (inside the group) with a (cutting) component, and then put that component onto its own layer, and then finally turn off that layer, the component will disappear, but the hole that it cuts in the surface will remain. To get rid of the hole I have to select the surface inside the group. It's quite annoying, as I like to use component (on their own layers) to model potential locations for doors and windows, and use layers (via scenes) to switch between them. But as soon as I put the surface inside groups I get these annoying ghost holes left behind by each component that is no longer visible because its layer has been turned off.

Steps to reproduce:

1. create a surface
2. create a group containing that surface
3. click into that group
4. cut a hole in the surface with a component
5. assign the component to a new layer
6. leave the group
7. turn off the component's layer
8. observe an annoying hole where the component used to be.
9. click into the group again
10. observe that the hole has disappeared.

Note: this only happens when the surface being cut is within a group (or component) of its own.

I found 7.1.6859 (free) for mac (based on Aerilius' post):

http://dl.google.com/sketchup/gsu7/FM-2-1-6859-EN.dmg

(what a relief: I've been trying to find it for ages!)

pro would be similarly:

http://dl.google.com/sketchup/gsu7/PM-2-1-6859-EN.dmg

Mike