diff --git a/src/db/db/db.pro b/src/db/db/db.pro
index 0b2eaeaeb..ef6d26aa5 100644
--- a/src/db/db/db.pro
+++ b/src/db/db/db.pro
@@ -292,7 +292,8 @@ HEADERS = \
     dbLayoutToNetlistWriter.h \
     dbLayoutToNetlistFormatDefs.h \
     dbDeviceAbstract.h \
-    dbLocalOperationUtils.h
+    dbLocalOperationUtils.h \
+    dbDeepRegion.h
 
 !equals(HAVE_QT, "0") {
 
diff --git a/src/db/db/dbHierProcessor.cc b/src/db/db/dbHierProcessor.cc
index 21729cb86..c84236f9d 100644
--- a/src/db/db/dbHierProcessor.cc
+++ b/src/db/db/dbHierProcessor.cc
@@ -772,6 +772,23 @@ LocalProcessorResultComputationTask::perform ()
   //  erase the contexts we don't need any longer
   {
     tl::MutexLocker locker (& mp_contexts->lock ());
+
+#if defined(ENABLE_DB_HP_SANITY_ASSERTIONS)
+    std::set<const db::LocalProcessorCellContext *> td;
+    for (db::LocalProcessorCellContexts::iterator i = mp_cell_contexts->begin (); i != mp_cell_contexts->end (); ++i) {
+      td.insert (&i->second);
+    }
+    for (db::LocalProcessorContexts::contexts_per_cell_type::iterator pcc = mp_contexts->context_map ().begin (); pcc != mp_contexts->context_map ().end (); ++pcc) {
+      for (db::LocalProcessorCellContexts::iterator i = pcc->second.begin (); i != pcc->second.end (); ++i) {
+        for (db::LocalProcessorCellContext::drop_iterator j = i->second.begin_drops (); j != i->second.end_drops (); ++j) {
+          if (td.find (j->parent_context) != td.end ()) {
+            tl_assert (false);
+          }
+        }
+      }
+    }
+#endif
+
     mp_contexts->context_map ().erase (mp_cell);
   }
 }
@@ -892,6 +909,23 @@ void LocalProcessor::compute_contexts (LocalProcessorContexts &contexts,
 
     db::LocalProcessorCellContexts &cell_contexts = contexts.contexts_per_cell (subject_cell, intruder_cell);
 
+#if defined(ENABLE_DB_HP_SANITY_ASSERTIONS)
+    if (subject_parent) {
+      db::LocalProcessorContexts::contexts_per_cell_type::iterator pcc = contexts.context_map ().find (subject_parent);
+      if (pcc == contexts.context_map ().end ()) {
+        tl_assert (false);
+      }
+      tl_assert (pcc->first == subject_parent);
+      bool any = false;
+      for (db::LocalProcessorCellContexts::iterator pcci = pcc->second.begin (); pcci != pcc->second.end () && !any; ++pcci) {
+        any = (&pcci->second == parent_context);
+      }
+      if (!any) {
+        tl_assert (false);
+      }
+    }
+ #endif
+
     cell_context = cell_contexts.find_context (intruders);
     if (cell_context) {
       //  we already have a context for this intruder scheme
@@ -1087,23 +1121,24 @@ LocalProcessor::compute_results (LocalProcessorContexts &contexts, const LocalOp
       std::vector<db::cell_index_type> next_cells_bu;
       next_cells_bu.reserve (cells_bu.size ());
 
-      std::list<LocalProcessorResultComputationTask *> tasks;
-
       for (std::vector<db::cell_index_type>::const_iterator bu = cells_bu.begin (); bu != cells_bu.end (); ++bu) {
 
-        if (later.find (*bu) == later.end ()) {
+        LocalProcessorContexts::iterator cpc = contexts.context_map ().find (&mp_subject_layout->cell (*bu));
+        if (cpc != contexts.context_map ().end ()) {
+
+          if (later.find (*bu) == later.end ()) {
 
-          LocalProcessorContexts::iterator cpc = contexts.context_map ().find (&mp_subject_layout->cell (*bu));
-          if (cpc != contexts.context_map ().end ()) {
             rc_job->schedule (new LocalProcessorResultComputationTask (this, contexts, cpc->first, &cpc->second, op, output_layer));
             any = true;
-            for (db::Cell::parent_cell_iterator pc = cpc->first->begin_parent_cells (); pc != cpc->first->end_parent_cells (); ++pc) {
-              later.insert (*pc);
-            }
+
+          } else {
+            next_cells_bu.push_back (*bu);
+          }
+
+          for (db::Cell::parent_cell_iterator pc = cpc->first->begin_parent_cells (); pc != cpc->first->end_parent_cells (); ++pc) {
+            later.insert (*pc);
           }
 
-        } else {
-          next_cells_bu.push_back (*bu);
         }
 
       }
diff --git a/src/db/db/dbHierProcessor.h b/src/db/db/dbHierProcessor.h
index 4cba12d1b..5ed1ecb4e 100644
--- a/src/db/db/dbHierProcessor.h
+++ b/src/db/db/dbHierProcessor.h
@@ -103,6 +103,7 @@ class DB_PUBLIC LocalProcessorCellContext
 {
 public:
   typedef std::pair<const db::Cell *, db::ICplxTrans> parent_inst_type;
+  typedef std::vector<LocalProcessorCellDrop>::const_iterator drop_iterator;
 
   LocalProcessorCellContext ();
   LocalProcessorCellContext (const LocalProcessorCellContext &other);
@@ -130,6 +131,18 @@ public:
     return m_lock;
   }
 
+  //  used for debugging purposes only
+  drop_iterator begin_drops () const
+  {
+    return m_drops.begin ();
+  }
+
+  //  used for debugging purposes only
+  drop_iterator end_drops () const
+  {
+    return m_drops.end ();
+  }
+
 private:
   std::unordered_set<db::PolygonRef> m_propagated;
   std::vector<LocalProcessorCellDrop> m_drops;
diff --git a/src/db/db/dbNetlistDeviceExtractorClasses.cc b/src/db/db/dbNetlistDeviceExtractorClasses.cc
index 79f344f94..a82fa11ff 100644
--- a/src/db/db/dbNetlistDeviceExtractorClasses.cc
+++ b/src/db/db/dbNetlistDeviceExtractorClasses.cc
@@ -109,6 +109,11 @@ void NetlistDeviceExtractorMOS3Transistor::extract_devices (const std::vector<db
         //  count the number of gate shapes attached to this shape and distribute the area of the
         //  diffusion region to the number of gates
         int n = rgates.selected_interacting (db::Region (*d)).size ();
+        if (n == 0) { // @@@@
+          printf("@@@ p=%s\n", p->box().to_string().c_str());
+          printf("@@@ rdiff=%s\n", rdiff.to_string().c_str());
+          printf("@@@ rgates=%s\n", rgates.to_string().c_str()); fflush(stdout);
+        }
         tl_assert (n > 0);
 
         device->set_parameter_value (diff_index == 0 ? db::DeviceClassMOS3Transistor::param_id_AS : db::DeviceClassMOS3Transistor::param_id_AD, dbu () * dbu () * d->area () / double (n));