Taking an HTTP server's resulted in WiFi connection failures

The situation:

I have a server that only serves HTTP with an assigned IP. My firewall forwards all HTTP requests to an external address to this server's IP.

I foolishly changed the MAC assigned to this IP address to my own machine as we were clearing out stale assignments and it wasn't responding to ping.

This morning, our guest WiFi could not reach any outside addresses. Our other two wireless networks would take several minutes to get an IP, could barely communicate with any internal addresses and could reach not outside addresses.

• A wired connection did not have this problem.
• The wireless is not on a separate VLAN.
• When I checked the server from it's other IP, it did not have an IP assigned to the NIC whose IP I stole.

It was mentioned in a comment when I posted this in sysadmin that it was due to ARP cache, but, again, it only affected wireless clients.

Changing the MAC back fixed the issue. I'd like to understand the how/why only wireless clients were behaving this way.