As part of our bridge loop avoidance, our APs send out gratuitous ARP packets beginning with MACs BA:BE. These packets should be dropped by the LAN equipment, but in some cases we've found that the LAN devices will actually accept them, which can cause trouble for the network.
In this situation we recommend taking the following steps:
Check what features the switch/router is using that could cause it to retain Gratuitous ARP packets. Some switches have flood protection or other ARP features that may cause them to create ARP entries they shouldn't. Check the manual specifically for any mention of "Gratuitous ARP".
Enable the VLANs outlined in the article How to Configure Switches for Seamless Roaming