@rene26 , I can confirm your findings.

I just was fiddling with my network for a day now. At least I decided to install the firmware and the effects have gone.

  @David-TP 

Thanks David for following up on this issue.

I didn't change anything on my network except the firmware upgrade of the TP-Link repeater. After I identified the issue I turned off all network components (router, switch, APNs and the repeater) and started them again to clear all ARP caches. It took about 4-8 hours and the error with the TP-Link repeater occurred again replying for IP addresses that are not registered in the repeater network.

After going back to the old firmware the issue didn't occur any longer (for about a week right now).

If I have some time during the weekend I can try the upgrade to the latest firmware version again to see if I can reproduce it once more.

  @David-TP 

Thx for the quick reply.

For further investigations it would help to state the behaviour intended.

A minimal system consists of three devices: a router with DHCP server, a repeater ( DHCP off ), a device.

Device has MAC x, repeater has MAC y.

What MACs are sent to the DHCP server in requests of repeater and device?

Which MACs are used for ARP packets?

Which MACs are used in the 802.11 packets?

All these questions can be answered by investigation of an existing system. But without the knowledge of the goals of the implementation these results can't be qualified ( a verfication isn't possible without knowing the code ).

For simple administration of a network following conditions should be true:

1) MACs are unique IDs for a device

2) MACs do not depend on the way of packets between router and device

Condition 2 is necessary for identification of a device by the router. Especially for functionalities DHCP server, access control, firewall.