Comment 3 for bug 701953

Note that legitimate bzr operations (most obviously 'push --overwrite' of an uncommit, but there are others) can cause a previous valid revno to no longer exist. So there will be cases where Launchpad offers a link to see revision number X, and then by the time the user follows that link the revision numbered X no longer exists. I doubt we can do better than 404 (perhaps with a helpful link to branch itself, which probably still does exist, although of course branches can be deleted!)

I *think* this may be a duplicate of a older bug report, but I might be misremembering.

Setting the append_revisions_only flag on a branch (which might become the default bzr behaviour for new branches one day?) would prevent this situation (until the user unsets the flag…).