There is a bug in the latest 4.7.3.X version. I haven’t been able to test 4.7.4. 
 

One person locked and unpinned a topic and their user name was shown in the topic as expected as doing so.
 

I came by and reversed the locking action and now the topic says that I am the one who both unpinned/locked the topic and then subsequently unlocked it, replacing the previous persons name.

Just an FYI that I have split this from the previous topic you posted under as the issues were unrelated. 🙂

Please let us know once you have tested this on the latest release of the platform. We can then take a look at that point if you are seeing the same issue