My Pi Hole displays te wrong IP for itself under Settings > System.
I did a fresh install of Raspbian Light Stretch the other day, still using my old router with the IP range of 192.168.1.0 for DHCP. I did setup a static IP for the PI (/etc/dhcpcd.conf) namely 192.168.1.3. Later I installed a new router, which uses the 192.168.178.0 range by default so I decided to stick with that. Assigned a static IP: 192.168.178.3 and rebooted and all is well. Works just fine for all devices, but the Settings > System on the Pi WebGUI still displays it’s old IP (192.168.1.3). I did reboot the Pi a few times and cleared browser cache, but to no avail.
It's neither aggressive nor a bug. With that reconfigure you just assign the new IP to Pi-hole - there is no auto-detect & auto-change to a new IP in Pi-hole.