code review has no way to force regenerating Review diff

There doesn't seem to be a way to tell the code review page that the diff needs to be regenerated.

It is possible to get a small race condition for the patch previews, as evidenced by:
https://code.edge.launchpad.net/~jameinel/bzr/1.16-simple-win32/+merge/6984

My guess of what happened is that:

1) Vincent landed his patch about 'stderr' to http://bazaar-vcs.org/bzr/bzr.dev
2) I branched from that, and made my fix
3) I pushed up my fix, and requested a review
4) Code-review generated the "Review Diff"
5) Launchpad then mirrored http://bazaar-vcs.org/bzr/bzr.dev => lp:bzr

At that point the Review diff ends up including a patch which isn't actually special for my change.
The weirdest part is that the list of revisions being merged is "correct" in that it only shows the single revision that is actually my change. But it certainly has the wrong diff associated with that change.

I don't think there is an easy way to avoid the race condition, so adding a "regenerate the diff" option would be nice. Another option would be to have code that notices that *some* of the revisions proposed for merge have actually landed in the development focus, and have it automatically detect that the diff needs to be regenerated.