When you specify a netmask, Squid checks your work. If your netmask masks out non-zero bits of the IP address, Squid issues a warning. For example, the following lines results in the subsequent warning:
acl Foo src 127.0.0.1/8
aclParseIpData: WARNING: Netmask masks away part of the specified IP in 'Foo'
The problem here is that the /8 netmask (255.0.0.0) has all zeros in the last three octets, but the IP address 127.0.0.1 doesn't. Squid warns you about the problem so you can eliminate the ambiguity. To be correct, you should write:
acl Foo src 127.0.0.1/32
or:
acl Foo src 127.0.0.0/8