Or does the gui have special powers the API doesn't?

In order to move one or more volumes into PODS, you can either create a new unstretched POD _*or*_ – and this can be tricky – you need to unstretch an existing POD first. If a POD contains volumes that are actually being accessed on both sites, you need the hosts to stop using the volumes on the array that’s going to be deleted from the POD for a short while.