I'm with Iku Rex. Shadow blur only works in shadow (or total darkness) anyway, so anytime you're shadow blurred you'd also be able to hide in plain sight.
All this nonsense about it being "your own shadow" or not is irrelevant.
They mean they cannot hide in shadows cast by light shining on them. This is an effect that seems to conjure shadows in an emination centered on you. Its not "your shadow" in the sense that its a shadow created by your physical presense in the normal way, merely in the sense that it "belongs" to you. However, so would wearing an item that eminates the darkness spell.