Steps to reproduce

1) Create a review for the file using a light SCM plugin
2) Immediately after creating, when the file says "Updating" next to the file name, click on "edit revisions" and choose a previous revision.
3) The chosen revision will not be added to the review, instead a new file (same filename) will be added with the chosen revision.

If when adding the file to the review you wait for a few seconds, until the updating becomes "modified", then you can edit revisions and add a previous revision and it will be added to the existing file as expected.