diff --git a/src/libslic3r/Geometry.cpp b/src/libslic3r/Geometry.cpp
index db64f97a7f..4cf4b5caa7 100644
--- a/src/libslic3r/Geometry.cpp
+++ b/src/libslic3r/Geometry.cpp
@@ -1182,19 +1182,27 @@ Transform3d assemble_transform(const Vec3d& translation, const Vec3d& rotation,
 Vec3d extract_euler_angles(const Eigen::Matrix<double, 3, 3, Eigen::DontAlign>& rotation_matrix)
 {
 #if ENABLE_NEW_EULER_ANGLES
-    // see: http://www.gregslabaugh.net/publications/euler.pdf
+    // reference: http://www.gregslabaugh.net/publications/euler.pdf
     auto is_approx = [](double value, double test_value) -> bool { return std::abs(value - test_value) < EPSILON; };
 
     Vec3d angles1 = Vec3d::Zero();
     Vec3d angles2 = Vec3d::Zero();
     if (is_approx(std::abs(rotation_matrix(2, 0)), 1.0))
     {
-        // the handling of singular cases deviates from the cited paper
-        // the following code works better when rotating an object with the gizmo after having
-        // changed its orientation using the place on bed gizmo
         angles1(0) = 0.0;
-        angles1(1) = 0.5 * (double)PI;
-        angles1(2) = angles1(0) + ::atan2(rotation_matrix(0, 1), rotation_matrix(0, 2));
+        if (rotation_matrix(2, 0) > 0.0) // == +1.0
+        {
+            angles1(1) = 0.5 * (double)PI;
+            angles1(2) = angles1(0) + ::atan2(rotation_matrix(0, 1), rotation_matrix(0, 2));
+
+        }
+        else // == -1.0
+        {
+            angles1(1) = 0.5 * (double)PI;
+            angles1(2) = -angles1(0) - ::atan2(rotation_matrix(0, 1), rotation_matrix(0, 2));
+
+        }
+
         angles2 = angles1;
     }
     else
diff --git a/src/slic3r/GUI/GLCanvas3D.cpp b/src/slic3r/GUI/GLCanvas3D.cpp
index f124390632..4a149eea85 100644
--- a/src/slic3r/GUI/GLCanvas3D.cpp
+++ b/src/slic3r/GUI/GLCanvas3D.cpp
@@ -2726,7 +2726,20 @@ void GLCanvas3D::Selection::_synchronize_unselected_instances(bool including_z)
             if ((v->object_idx() != object_idx) || (v->instance_idx() == instance_idx))
                 continue;
 
-            v->set_instance_rotation(Vec3d(rotation(0), rotation(1), including_z ? rotation(2) : m_cache.volumes_data[j].get_instance_rotation()(2) + rotation(2)));
+            auto is_approx = [](double value, double test_value) -> bool { return std::abs(value - test_value) < EPSILON; };
+
+            double z;
+            if (including_z)
+                // rotation comes from place on face -> force given z
+                z = rotation(2);
+            else if (is_approx(rotation(0), m_cache.volumes_data[j].get_instance_rotation()(0)) && is_approx(rotation(1), m_cache.volumes_data[j].get_instance_rotation()(1)))
+                // z only rotation -> keep instance z
+                z = v->get_instance_rotation()(2);
+            else
+                // generic rotation -> update instance z
+                z = m_cache.volumes_data[j].get_instance_rotation()(2) + rotation(2);
+
+            v->set_instance_rotation(Vec3d(rotation(0), rotation(1), z));
             v->set_instance_scaling_factor(scaling_factor);
             v->set_instance_mirror(mirror);