There's a bug in creating links with LogJam. LogJam is incorrectly replacing '&' in URLs used to create links with '&'. I'm not sure when this bug was first introduced, but my memory says it's been around since at least 4.3.0. Don't know why I haven't mentioned it before.
The saving grace is, it's getting away with it because LiveJournal is apparently unmunging the URL again when the post is actually submitted. Nevertheless, better not to break it in the first place.