Static dhcp don't work sometimes

Installing and Using OpenWrt
1

I have the openwrt running on the hyperV, the host pc have two ethernet, one used in LAN and another in WAN.
In most time, I set a static dhcp for the LAN card, but sometimes, the LAN card will get another IP address, I don't know why.

config dnsmasq
	option domainneeded '1'
	option localise_queries '1'
	option rebind_protection '1'
	option rebind_localhost '1'
	option local '/lan/'
	option domain 'lan'
	option expandhosts '1'
	option authoritative '1'
	option readethers '1'
	option leasefile '/tmp/dhcp.leases'
	option resolvfile '/tmp/resolv.conf.auto'
	option nonwildcard '1'
	option localservice '1'

config dhcp 'lan'
	option interface 'lan'
	option start '100'
	option limit '150'
	option leasetime '12h'
	option ra 'server'
	option dhcpv6 'server'
	option ra_management '2'

config dhcp 'wan'
	option interface 'wan'
	option ignore '1'

config odhcpd 'odhcpd'
	option maindhcp '0'
	option leasefile '/tmp/hosts/odhcpd'
	option leasetrigger '/usr/sbin/odhcpd-update'
	option loglevel '4'

config host
        option name 'hyperv'
	option mac '00:E0:4C:68:18:F3'
	option ip '192.168.2.66'	
	option dns '1'