I was doing a bit more testing today regarding that locking & group notice error and one of the times I went back to unlock the test topic I went to Topic Properties instead of the usual direct link method.  The log correctly adds & shows the unlocked entry, but then it has an additional entry like this:

<Me> changed the subject of topic Airliner Modelling Digest (AMD) - Digest #303 from "Airliner Modelling Digest (AMD) - Digest #303", via web

I didn't change anything in the subject obviously.  I then tested it with just going into Topic Properties, changing nothing and clicking Update instead of Cancel and the same entry is added, so something in the Update process causes it.