This is what I understood so far on how Pull request process works in Kallithea. Once a pull request is created a common ancestor between Origin repository and Destination repository is conceived and the diff is calculated and shown based on this ancestor.
In case something is changed to the Origin repository of the pull request the Pull request page will show this and there will be an option to open an updated pull request (v2) and the previous pull request will be closed.
However if something is changed in the Destination repository no such information exists, which would be pretty interesting to know, since some time can pass before a Pull request is reviewed and there might be changes added to the Destination repo that are NOT show in the Pull request diff.
So is there a way to either change the ancestor to include the new changes made to the destination ( Which is what I would expect to work out of the box, since when I create a pull request I use a branch not a specific revision ), or add some kind of info like it's done when creating a pull request, where there is an information that tells if the Destination has some commits ahead of Origin.