Cisco 2901 and Windows Odd behavior

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We have a Cisco 2901 with multiple WICs and three of the Routing Interfaces
 are connected to the same single dumb switch.  

Obviously the interfaces should not normally be connecting to the same swit
ch, but that's how our system is currently designed.  

The odd thing is when a Windows PC (no IP yet) and another device (device A
,for example IP are both connected to this same dumb switch, wh
en we try to configure an IP on the Windows PC, the PC responds with IP add
ress conflict. We are sure there is no IP conflict, but the message comes u
p everytime.

Even though we can try any random IP on the Windows PC, it always responds  
with IP conflict.  

If I remove the three network cables from the router interfaces, with just  
the Windows PC and device A connected, I can configure the Windows PC IP wi
th no problem and communicate with device A. Ever after putting the cables  
back into the router, everything seems fine at that point.

So the problem seems to only appear when trying to set an IP on the PC, but
 once the IP is set, all seems well.  I'm certain it's not related to a tru
e IP conflict, but maybe something in the way Windows detects IP conflicts?

Maybe PC having the same MAC address across multiple interfaces causes this

Does anyone know why the PC would think there is an IP conflict when trying
 to set the IP?    

Very curious...

Thanks in advance!

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