[Exim] 'control = freeze' and 'freeze_tell = postmaster'

OK, maybe I'm daft in my reading of the spec, but here goes anyway.

I want to use 'control = freeze' in an ACL, and I want mail when it
happens. But with 'freeze_tell = postmaster' all I get is a message
telling me that it was frozen by the ACL, without any indication as to
why.

Secondly, the spec says about freeze_tell: 'The reason(s) for freezing
can be found in the message log.'. Well, I've fiddled with message and
log_message, and I don't see any of them in the message log. Warnings
does show up in the mainlog.

So throw me a bone here, is there a way to get the freeze
notifications to include a message from the ACL, or the message log,
and shouldn't the message log include a tad more than 'frozen by ACL'?

--
Thomas
beast@???