Question about MAC address in wireless network.

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
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