Hi, I'm having similar issue, but I'm using vCenter Server 5.1.0, 1473063 and same ESXi build as yours ESXi 5.1 build 1743533. My VMs are in customization loop and I can see imcXXX.tmp file in each VM datastore even after the customization. Which is technically wrong as imcXXX.tmp file should only be there for customization to run and after customization finished, it should be removed.
Please let me know if you've fixed your issue.
Regards