When the router boots up and OSPF is activated on an interface, it queries all OSPF speaking devices in a LAN for DR/BDR status. If none exists, it assume the DR role. A second router boots up on that same LAN and do the same, will find the current DR running on that segment and will assume the BDR role regardless of its OSPF priority and|or RouterID.
There is no preemption under OSPF, in other words, the second router won't take over the first router's assignment.
For that reason, if you want to ensure a router will always be the DR of a segment, you must change the OSPF priority on this router to 255 and all other routers to 0 so they won't participate on the election - regardless when they were booted up.
HTH,
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Edison.
