Editing the list of duplicates on a question bumps said question and appears as a revision in the questions revision history, there is no indication on the question page itself though.
So this is what you see on the homepage, with the user and timestamp of the edit:
This is what you see in the revision history:
On the question itself... nothing:
Seeing a post was edited on the homepage then opening it to see nothing has changed is pretty confusing. This is, as far as I know (?), now the only thing that will bump a question with no indication on the question itself (community bumps used to; they now have a notice).