[Exim] Auto_thaw and system_filter interaction?

Hello,

We are now using Nigels' system filter produced last week (many thanks Nigel
for producing that) and are thinking
of implementing a 24 hour "quarantine" area on our mail relay boxes only to
buffer possible problems like those
seen last week. We were hoping that by utilising the filters' "...and not
first_delivery" command and thawing using
"auto_thaw = 24h" that they would pass the filter by when thawed. However
what we are seeing is that the
messages are being thawed correctly but being picked up again by the filter.

Am I misunderstanding the meaning of "first_delivery" or am I missing
something else more obvious. Manually
thawed message get delivered as expected but are still evading being picked
up by "..and not first_delivery".

(Note: Exim 3.12, Solaris 2.5.1 & 7)

regards
Martyn Griffiths
Network Services Group
University of Glamorgan
UK