[exim] strange ACL expansion behaviour

Hello,

I am using exim 4.63 on a linux system (debian, but exim is compiled
from source).

I have this ACL:

accept
sender_domains = ${lookup{dwl}lsearch{/etc/blacklists.conf}}
set acl_m5 = OK
log_message = $sender_address_domain is locally whitelisted

In /etc/blacklists.conf
if I have:
dwl: domain1.com
it works

if I have
dwl: domain1.com:
it also works

if I have
dwl: domain1.com::
The ACL doesn't seem to work as the message is not accepted in this step.

Is this normal behaviour?

--
010100100110010101101110011000010111010101100100
010000010110110001101100011000010111001001100100