dnsmasq not responding DHCP requests that don't follow a DHCP discover

I have an instance of dnsmasq running on network namespace X, and I run dhclient (or any other dhcp client) from within network namespace Y to obtain an IP address on a given interface. The two network namespaces are on the same openvswitch bridge, through which they communicate.

I see that dnsmasq takes ages to reply, somewhere between 10 and 30 seconds, even if a tcpdump shows that all DHCP packets are promptly delivered to the destination namespace.

Why does it take so long? Is there a way to reduce this delay?

Here's an example from /var/log/syslog where the IP address is assigned after 11 seconds:

Apr  4 14:31:27 localhost dhclient: Listening on LPF/_0.ping/ae:ca:22:bc:3c:7b
Apr  4 14:31:27 localhost dhclient: Sending on   LPF/_0.ping/ae:ca:22:bc:3c:7b
Apr  4 14:31:27 localhost dhclient: Sending on   Socket/fallback
Apr  4 14:31:27 localhost dhclient: DHCPREQUEST on _0.ping to 255.255.255.255 port 67
Apr  4 14:31:33 localhost dhclient: DHCPREQUEST on _0.ping to 255.255.255.255 port 67
Apr  4 14:31:48 localhost dhclient: DHCPDISCOVER on _0.ping to 255.255.255.255 port 67 interval 3
Apr  4 14:31:48 localhost dnsmasq-dhcp[11719]: DHCPDISCOVER(_0.dhcp) 192.168.31.110 ae:ca:22:bc:3c:7b 
Apr  4 14:31:48 localhost dnsmasq-dhcp[11719]: DHCPOFFER(_0.dhcp) 192.168.31.110 ae:ca:22:bc:3c:7b 
Apr  4 14:31:48 localhost dhclient: DHCPREQUEST on _0.ping to 255.255.255.255 port 67
Apr  4 14:31:48 localhost dhclient: DHCPOFFER from 192.168.31.1
Apr  4 14:31:48 localhost dnsmasq-dhcp[11719]: DHCPREQUEST(_0.dhcp) 192.168.31.110 ae:ca:22:bc:3c:7b 
Apr  4 14:31:48 localhost dnsmasq-dhcp[11719]: DHCPACK(_0.dhcp) 192.168.31.110 ae:ca:22:bc:3c:7b mymachine
Apr  4 14:31:48 localhost dnsmasq-dhcp[11719]: not giving name mymachine to the DHCP lease of 192.168.31.110 because the name exists in /etc/hosts with address 127.0.0.1
Apr  4 14:31:48 localhost dhclient: DHCPACK from 192.168.31.1
Apr  4 14:31:48 localhost dhclient: ntp-servers: expecting at least 4 bytes; got 0
Apr  4 14:31:48 localhost dhclient: bound to 192.168.31.110 -- renewal in 33935 seconds.

The dnsmasq instance is launched with the following command:

dnsmasq --dhcp-range=set:tag0,192.168.31.100,192.168.31.150,24h -l /tmp/dnsmasq-leasefile.dhcp.dhcp --dhcp-option=tag:tag0,option:router,192.168.31.2 --dhcp-option=tag:tag0,option:dns-server,9.9.9.9 --dhcp-option=tag:tag0,42

EDIT Ok, I ran it a few more times and I think I see a pattern in there. The DHCP client starts by sending two DHCP requests, which are both unanswered. As soon as a DHCP discover is sent, dnsmasq replies. The reason why dhclient first tries with a DHCP request is that it sees a previous lease for the same interface in /var/lib/dhcp/dhclient.leases and tries requesting the IP address appearing there. As soon as I remove such file, the response from dnsmasq is generated instantly. I see two options:

• I tell dhclient not use its lease file (not sure how), but this is not really ideal...
• I instruct dnsmasq to respond to requests that don't follow a discover message. How can I do this?