globalauth log doesn't work if you don't append the global username with @global in the target field.
This is quite confusing for people don't knowing CentralAuth well; it also means that you can't see the entries of this log together with the other logs' entries for the same users, including global ones like the global rights log (gblrights), which doesn't require @global: https://meta.wikimedia.org/w/index.php?title=Special%3ALog&type=gblrights&page=User%3APathoschild
@global should still work as alias/redirect to the globalauth log for the user, to avoid breaking any old links to logs (or habits) with the change.

Version: unspecified
Severity: enhancement
URL: https://meta.wikimedia.org/w/index.php?title=Special%3ALog&type=globalauth&user=&page=User%3APathoschild%40global