It seems the ROS must store DHCP lease in NV ram. After rebooting it still has the same leases(Dynamic). I would like them to be cleared when doing a power cycle.
Found my solution after giving the wiki another look… I missed it the first time
Sub-menu: /ip dhcp-server config
Leases are always stored on disk on graceful shutdown and reboot. If they would be saved on disk on every lease change, a lot of disk writes would happen. There are no problems if it happens on a hard drive, but is very bad for Compact Flash (especially, if lease times are very short). To minimize writes on disk, all changes are saved on disk every store-leases-disk seconds. If this time will be very short (immediately), then no changes will be lost even in case of hard reboots and power losts. But, on CF there may be too many writes in case of short lease times (as in case of hotspot). If this time will be very long (never), then there will be no writes on disk, but information about active leases may be lost in case of power loss. In these cases dhcp server may give out the same ip address to another client, if first one will not respond to ping requests.
store-leases-disk (time | immediately | never; Default: 5min) How frequently lease changes should be stored on disk