Host migration issues esx 5.5

Hi Support,

I am facing a strange behavior with Esxi 5.5 and vcenter 5.1.

We have multiple Esxi in the cluster we did a host migration from ESXI1 to
ESXI2 it worked fine and VM was hosting in ESXi2,After some time I powered off
the VM and powered on again that time the VM was automatically moved back to
its old Esxi that is ESXi1 and started from there.

Any idea why its behaving like this.

Thanks

Anoop