[exim] Panic in nwildlsearch

This is probably just a failure in my reading the documentation, but I see the following error and I can't see why it's trying to open a file

14:43:22 27954 failed to open /'#.@wirefast.com when checking "/'#.@wirefast.com": No such file or directory

It's processing this condition in an ACL

         hosts   = ${lookup{$header_x-imf-override-originator:}nwildlsearch{/path/to/file}}

and the file contains

/'#.@wirefast.com 10.20.30.40

Now I can't see anything in the documentation that suggests nwildlsearch will try to open a file for a line/key stating with "/"

Am I missing something in the documentation, is it an undocumented feature or am I misinterpreting the error?

Neil Youngman