Question about MAC address in wireless network.

[kitepilot at kitepilot.com]

Imagine the next scenario: 

Firewall-----AP1 )))) BR2-----AP3 )))) BR4
             IP1      IP2     IP3      IP4
             MAC1     MAC2    MAC3     MAC4 

Say that I ping them all and take a reading of the arp table in firewall, 
there are 2 possibilities depending on the settings of BR2: 

I can see real MAC address as:
IP1 -> MAC1
IP2 -> MAC2
IP3 -> MAC3
IP4 -> MAC4 

Or I can see only one MAC address: 

IP1 -> MAC1
IP2 -> MAC2
IP3 -> MAC2
IP4 -> MAC2 

I can't remember the name of the parameter that produces this or the reason 
why it happens.
And I am tired...
Can someone please elaborate and publish references?
Thanks!
ET