Question about git log --merge option

Dear list:

Just encountered the --merge option for git log.

In the man page, it has the following explanation:
- After a failed merge, show refs that touch files having a conflict
and don't exist on all heads to merge.

I tried this option and get below results:

1. For a failed merge (with conflicts), if the conflicted file does
not exist on either side of the merge, the --merge option will return
the log from the other side.

2. If the conflicted file exists on both sides of the merge, the
--merge option will return the latest change on either side. (i.e: git
log -1 -- conflict_file / git log -1 --merge -- conflict_file may
return different results, whichever changed the latest)

I'm not sure whether above behavior is the unexpected result (cannot
find detailed explanation for --merge option online).

Thanks