[exim] CIDR mask matching behavior

Eximers,
I noticed some unexpected behavior in Exim when doing send IP address
checks in the SMTP ACL, and later on in the system filter.
In ACL's, you can specify CIDR masks on a non-network address.

IE you can have 10.10.10.15/24, which is valid as 10.10.10.15 would
fit inside a /24 under 10.10.10.0
However, in a system filter doing something like this:

${mask:$sender_host_address/24} is 10.10.10.15/24

Will not evaluate true, but it will work in the following:

${mask:$sender_host_address/24} is 10.10.10.0/24


I tried finding in the source code where the system filter does
netmask checking, but could only find the section where ACLs evaluate
netmasks.
Has anyone encountered this before, or is this working as intended in
the system filter?



--
Brent Jones
brent@???