When the author differs from the committer, GitPlugin seems to favor the committer over the author as "Trac Author". This has impact in the timeline, log, and various other locations.
GitPlugin seems to have this concept of "Trac Author" in addition to "git-author" and "git-committer", as can be seen on: http://sablecc.org/changeset/1a3b6173986aa9cfc694acba0ecbbb7e40028f22
There might be reasons why a project would like to show the committer name, instead of the author name, in the timeline and log to show committer activity. Yet, other projects might have very few, or even a single committer in their official repository, as encouraged by Git. In such a case, it might make more sense to show the real author name in the timeline and log.
I suggest using a configuration flag to chose which of the git-author or git-committer to use as "Trac Author", so that everybody is pleased.