Comment 4 for bug 209948

The fix is actually pretty trivial:

The _filter_revisions_touching_file_id just didn't handle the case where a parent could be referenced, but not already computed in the ancestry.

I'll put together a test, and submit it:
=== modified file 'bzrlib/log.py'
--- bzrlib/log.py 2008-03-28 03:54:40 +0000
+++ bzrlib/log.py 2008-04-18 17:37:53 +0000
@@ -479,6 +479,8 @@
             if rev in weave_modifed_revisions:
                 rev_ancestry.add(rev)
             for parent in parents:
+ if parent not in ancestry: # Ghost
+ continue
                 rev_ancestry = rev_ancestry.union(ancestry[parent])
         ancestry[rev] = rev_ancestry