DHCP - device gets IP w/o reservation

[opn_minded]

Hi there,

I have a strange issue regarding a device that gets an IP, but has no reservation set for it. First things first, I'm on opnSense 25.7.7_4. The device is a soundbar, that is connected via cable and once had 10.0.40.4 as IP reservation. Several months ago, I decided that this device doesn't need to be online anymore, so I removed it's reservation in KEA.

A couple days ago I found out that 10.0.40.4 is (still) ping-able, even though it has no IP reservation in KEA. When I disable the switch-port (where the soundbar is connected to), I can't ping that IP.

My (IoT) VLAN is defined as 10.0.40.0/24, with just a single IP (10.0.40.199/32) as pool.

In my understanding - if I haven't set up an IP reservation for a certain device (based on its MAC), this device shouldn't be able to obtain an IP and access subnets. Am I wrong or is this actually an issue?