diff --git a/src/libslic3r/Print.cpp b/src/libslic3r/Print.cpp
index 770d02a7c..d6f0d9e0d 100644
--- a/src/libslic3r/Print.cpp
+++ b/src/libslic3r/Print.cpp
@@ -686,9 +686,11 @@ static std::vector<PrintInstances> print_objects_from_model_object(const ModelOb
     trafo.copies.assign(1, Point());
     for (ModelInstance *model_instance : model_object.instances)
         if (model_instance->is_printable()) {
-            const Vec3d &offst = model_instance->get_offset();
-            trafo.trafo = model_instance->world_matrix(true);
-            trafo.copies.front() = Point::new_scale(offst(0), offst(1));
+            trafo.trafo = model_instance->world_matrix();
+            // Set the Z axis of the transformation.
+			trafo.copies.front() = Point::new_scale(trafo.trafo.data()[3], trafo.trafo.data()[7]);
+            trafo.trafo.data()[3] = 0;
+            trafo.trafo.data()[7] = 0;
             auto it = trafos.find(trafo);
             if (it == trafos.end())
                 trafos.emplace(trafo);
diff --git a/src/libslic3r/Print.hpp b/src/libslic3r/Print.hpp
index d2dc81755..3c2a87c74 100644
--- a/src/libslic3r/Print.hpp
+++ b/src/libslic3r/Print.hpp
@@ -135,14 +135,16 @@ public:
         bool invalidated = false;
         for (size_t i = 0; i < COUNT; ++ i)
             if (m_state[i].load(std::memory_order_relaxed) != INVALID) {
-                if (! invalidated) {
-                    mtx.unlock();
-                    cancel();
-                    mtx.lock();
-                    invalidated = true;
-                }
-                m_state[i].store(INVALID, std::memory_order_relaxed);
+                invalidated = true;
+                break;
             }
+        if (invalidated) {
+            mtx.unlock();
+            cancel();
+            for (size_t i = 0; i < COUNT; ++ i)
+                m_state[i].store(INVALID, std::memory_order_relaxed);
+            mtx.lock();
+        }
         return invalidated;
     }
 
diff --git a/src/libslic3r/PrintObject.cpp b/src/libslic3r/PrintObject.cpp
index 6527a7272..8f9146766 100644
--- a/src/libslic3r/PrintObject.cpp
+++ b/src/libslic3r/PrintObject.cpp
@@ -1604,8 +1604,8 @@ std::vector<ExPolygons> PrintObject::_slice_volumes(const std::vector<float> &z,
             mesh.merge(v->mesh);
         if (mesh.stl.stats.number_of_facets > 0) {
             mesh.transform(m_trafo.cast<float>());
-            // align mesh to Z = 0 (it should be already aligned actually) and apply XY shift
-            mesh.translate(- unscale<float>(m_copies_shift(0)), - unscale<float>(m_copies_shift(1)), - float(this->model_object()->bounding_box().min(2)));
+            // apply XY shift
+            mesh.translate(- unscale<float>(m_copies_shift(0)), - unscale<float>(m_copies_shift(1)), 0);
             // perform actual slicing
             TriangleMeshSlicer mslicer;
             const Print *print = this->print();