when a TAP device is opened the Linux kernel assigns a random IP address; if this IP address is not-so-random then there's something funny going on with your ARM based kernel. Perhaps the entropy pool, used for generating random numbers, is not large enough or not filled correctly when the system starts.
You can hardwire the MAC address for a tap device using
lladdr AA:BB:CC:DD:EE:FF
but you'll need to do this for every client.
