Looking at issue #639 this seems to be the root cause

After fixing this part, there also needs to be made a change to the
example given or the schema of aws_elb.

terraform/graph.go

@@ -1816,21 +1816,23 @@ func (n *GraphNodeResource) expand(g *depgraph.Graph, count int, diff *ModuleDif
 				delete(keys, name)
 			}
 
-			if state == nil {
 			if count == 1 {
 				// If the count is one, check the state for ".0"
 				// appended, which might exist if we go from
 				// count > 1 to count == 1.
 				k := r.Id() + ".0"
+				if state == nil {
 					state = n.State.Resources[k]
+				}
 				delete(keys, k)
 			} else if i == 0 {
 				// If count is greater than one, check for state
 				// with just the ID, which might exist if we go
 				// from count == 1 to count > 1
+				if state == nil {
 					state = n.State.Resources[r.Id()]
-					delete(keys, r.Id())
 				}
+				delete(keys, r.Id())
 			}
 		}