Outgoing masquerade address changes after adding a second interface to the bridge

In fact I have the following configuration:

extrouter(192.168.1.1) <- wifi -> [eth2 (192.168.1.11) Centos 6/6 based host br0 (172.22.5.254)]

br0 contains two tap interfaces (tap0/172.22.5.1 tap1/172.22.5.2) from virtual machines (kvm), the gw inside VMs is 172.22.5.254.

If only a single virtual machine is connected to br0 all works well. I cant ping from VM 192.168.1.1 and tcpdump for eth2 shows 192.168.1.11 as outgoing address, masquerading works as expected. But if I add the second VM (the order of VMs are not important) the outgoing address changes to the 172.22.5.254. After removing one of VM from the bridge all goes back and starts working again.

Bridge has its own mac address, so adding an interface shouldn't change anything.

Any ideas what may be wrong?