I recently installed ESX 3.5 and was working with a pair of VMs - one Centos 5, one win2k3.
Both were assigned to the same virtual network with one interface. I originally assigned an IP to the win2k3 VM, but needed to migrate this IP to the Centos VM so I shut down the win2k3 guest OS, and the VM was stopped at this point. However I was unable to assign that IP to my Centos machine because it was determining that particular IP was in use on the network.
I started the win2k3 VM again and assigned it a different IP and left it running.
I was still unable to assign the IP to the Centos machine. Eventually I actually removed the NIC from the win2k3 VM, at which point I could assign the IP address to the Centos.
Was the virtual switch both these guests were attached to responding the the arping request from the Centos machine for some reason?
I think you should report this to VMware via your Support Specialist. They will want to fix this, or verify how it can be caused. I have never heard of something like this on a vSwitch.
Edward L. Haletky
VMware Communities User Moderator
Author of the book 'VMWare ESX Server in the Enterprise: Planning and Securing Virtualization Servers', Copyright 2008 Pearson Education. As well as the Virtualization Wiki at http://www.astroarch.com/wiki/index.php/Virtualization
... and the fun begins since I am evaluating the product!