Task Comment “posted by named person” will be missing IF you reply from a different email address
If you reply to a task notification by email and this becomes a comment in the task
The posted by NAME will be missing from the comment thread IF you reply from a different email address
eg this
Posted by Sally Jones 05/04/12 11:53
would read
Posted by 05/04/12 11:53
Related article: Not Getting Task Comments by Email (read here)