For the final explosion:

diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index 55b3e52..4c7cd24 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -454,6 +454,8 @@ void i915_gem_context_fini(struct drm_device *dev)
                        i915_gem_context_unreference(dctx);
                        dev_priv->ring[RCS].last_context = NULL;
                }
+
+               i915_gem_object_ggtt_unpin(dctx->obj);
        }
 
        for (i = 0; i < I915_NUM_RINGS; i++) {
@@ -466,7 +468,6 @@ void i915_gem_context_fini(struct drm_device *dev)
                ring->last_context = NULL;
        }
 
-       i915_gem_object_ggtt_unpin(dctx->obj);
        i915_gem_context_unreference(dctx);
 }

Works like a charm, thanks for spotting this quickly and please submit to intel-gfx.

commit d3b448d9917a3d6531e499d88bfb13ea5e31e4ad
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Fri May 16 18:59:00 2014 +0100

    drm/i915: Only unpin the default ctx object if it exists