D-Link router randomly changes IP addresses, why?

This is kind of complicated but I'll try to simplify it. A client (this is at a home residence) has a D-Link DIR-628 router. This is on the top floor. Its a tri-level home so they're having difficulty getting signal to the machine in the basement and sometimes the wireless printer kicks off or the netbook. The signal strength is weak probably due to walls and floors (its at 35% on average). So they bought a repeater. After endless labor this finally worked. For the longest time I could get on the network through it but no internet access. I finally found out this was because the router was assigning the repeater a 169 IP as opposed to the normal range of 168.xxxx addresses. It does the same thing to the printer on occasion and so far the only reason they've found to fix it is to reset the power on the router. We finally did this and it gave us internet on the repeater as well. So I haven't dug into the router too much yet but I don't know why it would sporadically kick out incorrect IP addresses to the repeater or printer. Currently everything is working but I have a feeling that will be temporary. I was working late and forgot to check the IP range its sending out, other than that I'm not sure why this would happen. Thoughts?