The JPEG image has insufficient information to tell.
Here are two possibilities:
A. Maybe someone has started a reply and then changed the subject.
It does happen.
Some people even start a reply and then change the subject and
body to make them look like a new message. They think this is
the same as starting a new post. The full headers will still
show it as a reply (Message-ID, References, and In-Reply-To).
B. It might be a hash collision between message IDs or between
subject lines.
https://groups.google.com/forum/?hl=en-GB#!topicsearchin/alt.usenet.offline-reader.forte-agent/%22hash$20collision%22
Actual information required to tell would include the following.
1. Your settings for the following three Agent settings:
1.1 [ ] Enable threading by subject
1.2 [ ] Start a new thread when a follow-up subject changes
1.3 Reply prefixes: [________________]
In Agent 4.2, these settings are at
"Tools >> Options >> Display >> Message List Pane"
2. The actual Message-ID, References , and In-Reply-To headers
from these messages.
This is needed to check for
* Whether the message was started as a reply;
* Whether there is a hash collisions between message IDs.
3. The exact actual subject line from these messages.
This is needed to check for
* hash collisions between subject lines
> FWIW, the communication is with the same email address that featured
> in my recent post 'No trace after a send', but that may be just
> coincidence.
--
Kind regards
Ralph