Airport Extreme breaks MAC-addresses?

[GenieonWork]

I've a weird problem here.

I've connected 10 IMAC's wireless to an Airport Extreme (firmware 7.5.2)
On the Airport, it lists the MAC-addresses of the clients correct.
However, on the DHCP-server I see all kind of weird MAC-addresses for those clients:
494d414331
494d414332
494d414333
494d414335
494d414336
494d414337
494d414339
494d41433130

This is what I tried:
MAC-address 494d434332 had in TCP-settings IMAC2 as being the hostname (I noticed the machines had their IMAC-number as the last character of the weird MAC-address).
I changed the DHCP client ID to TimV, resulting in the MAC-address changing to 54696d56.
After that, I changed the computername in the Sharing-settings to TimV, having no effect on the MAC-address (it just changed the host-name in the DHCP lease pool).

Anyone any idea plz?
I need those IMAC's have reservations, but I can't manage to do so now. And I don't want to set them all up with static IP-addresses...

 

[GenieonWork]

Solved; DHCP Client ID breaks it down.

I found out that when I fill in a DHCP Client ID, the MAC-address gets broken down.
I removed those entries from all the iMAC's, and now it's all working.

Still don't know why it does so by the way.
But at the moment, my problem is 'solved' (or should I say: Worked around?).