The DG refusing to cast until moving bug I have found is so far guaranteed for me when I try to use an ability after a DG has moved through my own. My friend has tried this aswell and had the same results. I'll give an example:
-I move within attack range of an Unclean Beast with my Erebus.
-I start melee attacking without moving my DG.
-The Unclean Beast walks directly through my own DG.
-I try to cast Bite and nothing happens until I physically move him and cast it again.
This has happened 100% of the time on the few gods I have tested it on Queen of Thorns, Sedna, Erebus and Unclean Beast haven't gotten round to the others I imagine there will be no difference.