This would be a bug in LJ because it could cause others to edit a post they don't own. But it could also be a "feature" in that LogJam did retrieve the last post entered in the particular community's journal.
Some kind of sanity checking needs to be performed to insure the poster always owns the post being retrieved under these circumstances, perhaps on both sides. It still might be satisfactory to retrieve someone else's post from a community for reading only.