iRule RAM CACHE odd behaviour

See if this makes a difference - explicitly enabling/disabling CACHE from HTTP_RESPONSE - apologies in advance - I have taken some liberties with the format of your original iRule (although retained the logic I hope);-

when HTTP_REQUEST {
    set fCache 0
    switch -glob [string tolower [HTTP::host]] {
        "someURL.test.co.uk"  {
            if { !([class match [IP::remote_addr] equals CUST_IP_Addresses])
            and !([class match [IP::remote_addr] equals MIC_IP_Addresses])
            and !([class match [IP::remote_addr] equals private_net]) } {
                drop 
                return
            } else {
                CACHE::disable
                pool "CUST-someURL.test.co.uk_[TCP::local_port]_POOL"
                return
            }
        }
        "someAURL.test.co.uk" {
            pool "CUST-someAURL.test.co.uk_[TCP::local_port]_POOL"
        }
        "*test.co.uk" {
            pool "CUST-www.test.co.uk_[TCP::local_port]_POOL"
        }
        "*test1.co.uk" {
            pool "CUST-test1.co.uk_[TCP::local_port]_POOL"
        } 
        default {
            pool "CUST-test2.co.uk_[TCP::local_port]_POOL"
        }
    }

    switch [getfield [string tolower [URI::basename [HTTP::path]]] "." 2] {
        "js" -
        "pdf" -
        "css" -
        "jpg" -
        "png" {
             enable the cache
            CACHE::enable
            set fCache 1
        }       
        default {
             disable the cache
            CACHE::disable
        }
    }
}
when HTTP_RESPONSE {
    if {$fCache} {
        CACHE::enable
    } else {
        CACHE::disable
    }
}