Sorry, my example wasn't very helpful in that respect. Yes, you are right about it controlling the cache capacity. However, even when I set it to large values (100, 1000, 100000 etc) it makes no difference.

After some digging around in the code for LWP::UserAgent (5.835) I found this

sub clone
{
    my $self = shift;
    my $copy = bless { %$self }, ref $self;  # copy most fields

    delete $copy->{handlers};
[download]

    # copy any plain arrays and hashes; known not to need recursive co
+py
    for my $k (qw(proxy no_proxy requests_redirectable)) {
        next unless $copy->{$k};
        if (ref($copy->{$k}) eq "ARRAY") {
            $copy->{$k} = [ @{$copy->{$k}} ];
        }
        elsif (ref($copy->{$k}) eq "HASH") {
            $copy->{$k} = { %{$copy->{$k}} };
        }
    }

    if ($self->{def_headers}) {
        $copy->{def_headers} = $self->{def_headers}->clone;
    }

    # re-enable standard handlers
    $copy->parse_head($self->parse_head);

    # no easy way to clone the cookie jar; so let's just remove it for
+ now
    $copy->cookie_jar(undef);

    $copy;
}
[download]

So it looks like the conn_cache data is not inherited when the UserAgent is cloned.

If I comment this line out (delete $copy->{conn_cache};), my problems go away. Could a more enlightened member tell me whether or not this looks like a bug, or am I just barking mad and fiddling with something with terrible unintended consequences?

Cheers
LB