[Exim] Message frozen but not frozen ?

This morning, I found the message below in my inbox. It seems to be
lying - the message isn't in the queue. I don't have auto_thaw
(unless it's enabled by default).

Log entries are below.

A related piece of information is that at 00:09 the mail system gets
shut down for backups to take place. This is done by sending a
SIGTERM to every Exim process running, pretty much simultaneously.

Ian.

-chiark:exim> grep 11OTt8-00088k-00 mainlog
1999-09-07 23:38:54 11OTt8-00088k-00 <= rocksoc-chat-admin@??? H=localhost (chiark.greenend.org.uk) [127.0.0.1] U=list P=esmtp S=2626 id=Pine.SOL.4.10a.9909072333220.3215-100000@???
1999-09-07 23:38:54 11OTt8-00088k-00 => [ some subscriber at demon ] R=lookuphost T=smtp H=punt-1.mail.demon.net [194.217.242.35] C="250 Submitted & queued (30/msg.aa1000b585)"
...
1999-09-07 23:38:59 11OTt8-00088k-00 => [ some subscriber at freeserve ] R=lookuphost T=smtp H=mail-in.pol.net.uk [195.92.193.24] C="250 OK id=11OTtD-0005wP-00"
1999-09-07 23:43:01 11OTt8-00088k-00 Spool file is locked
1999-09-07 23:52:03 11OTt8-00088k-00 murphys.force9.net [195.166.128.122]: Connection timed out
1999-09-07 23:52:25 11OTt8-00088k-00 Spool file is locked
1999-09-08 00:03:01 11OTt8-00088k-00 Spool file is locked
1999-09-08 00:05:12 11OTt8-00088k-00 medusa.plus.net.uk [195.166.128.97]: Connection timed out
1999-09-08 00:09:03 11OTt8-00088k-00 == JOHNSMITH@??? T=smtp defer (-1): smtp transport process returned non-zero status 0x000f: terminated by signal 15
1999-09-08 00:09:03 11OTt8-00088k-00 Frozen
1999-09-08 00:09:03 11OUMJ-00006t-00 <= <> R=11OTt8-00088k-00 U=mail P=local S=618
1999-09-08 00:22:30 11OTt8-00088k-00 murphys.force9.net [195.166.128.122]: Connection timed out
1999-09-08 00:23:01 11OTt8-00088k-00 Spool file is locked
1999-09-08 00:31:39 11OTt8-00088k-00 guiness.force9.net [195.166.128.113]: No route to host
1999-09-08 00:39:16 11OTt8-00088k-00 Spool file is locked
1999-09-08 00:43:02 11OTt8-00088k-00 Spool file is locked
1999-09-08 00:44:48 11OTt8-00088k-00 medusa.plus.net.uk [195.166.128.97]: Connection timed out
1999-09-08 00:57:57 11OTt8-00088k-00 caffreys.force9.net [195.166.128.121]: Connection timed out
1999-09-08 00:57:57 11OTt8-00088k-00 mx1.plus.net.uk [195.166.128.26]: Connection refused
1999-09-08 00:58:00 11OTt8-00088k-00 => JOHNSMITH@??? R=lookuphost T=smtp H=mx2.plus.net.uk [195.166.128.27] C="250 ok 936748629 qp 7629"
1999-09-08 00:58:00 11OTt8-00088k-00 Completed
-chiark:exim>

Message 11OTt8-00088k-00 has been frozen. The sender is <rocksoc-chat-admin@???>.

The following address(es) have yet to be delivered:
JOHNSMITH@???: smtp transport process returned non-zero status 0x000f: terminated by signal 15