When I last upgraded from Firmware 4.4x with "Keep Settings",.. DHCP randomly started assigning different IP addresses to existing devices outside of DHCP reserved range (see this thread)
my settings was:
192.168.0.99 (manually changed router IP)
192.168.0.100 - 192.168.0.249 (Manually Set DHCP range)
192.168.0.120 (121,122,123,124 etc had Reserved IPs)
However, after upgrade, some devices which had reserved IPs started getting new IPs
192.168.0.1, 192.168.0.5, 192.168.0.3 etc,... (which was Not right and also, these devices couldn't access internet).
So Now, after Not keeping settings while upgrading,.. DHCP is working normally thus far (not like before,.. randomly assigning addresses mentioned above)
All this means,.. there are bugs in "Keep Settings" somewhere after 4.4x firmwares?