diff --git a/apps/variable_box_controller.cpp b/apps/variable_box_controller.cpp
index 6e3e871a3..7d8207625 100644
--- a/apps/variable_box_controller.cpp
+++ b/apps/variable_box_controller.cpp
@@ -170,7 +170,7 @@ KDCoordinate VariableBoxController::ContentViewController::rowHeight(int index)
   }
   LayoutRef layoutR = layoutRefForIndex(index);
   if (!layoutR.isUninitialized()) {
-    return layoutR.layoutSize().height()+k_leafMargin;
+    return max(layoutR.layoutSize().height()+k_leafMargin, Metric::ToolboxRowHeight);
   }
   return Metric::ToolboxRowHeight;
 }
diff --git a/apps/variable_box_controller.h b/apps/variable_box_controller.h
index 05906cb93..14f450ed0 100644
--- a/apps/variable_box_controller.h
+++ b/apps/variable_box_controller.h
@@ -48,7 +48,7 @@ private:
 #else
     constexpr static int k_numberOfMenuRows = 2;
 #endif
-    constexpr static KDCoordinate k_leafMargin = 10;
+    constexpr static KDCoordinate k_leafMargin = 20;
     Page pageAtIndex(int index);
     void putLabelAtIndexInBuffer(int index, char * buffer);
     I18n::Message nodeLabelAtIndex(int index);
diff --git a/poincare/include/poincare/global_context.h b/poincare/include/poincare/global_context.h
index e4264280b..07848f207 100644
--- a/poincare/include/poincare/global_context.h
+++ b/poincare/include/poincare/global_context.h
@@ -28,7 +28,9 @@ private:
   static Decimal defaultExpression();
   int symbolIndex(const Symbol & symbol) const;
   Expression m_expressions[k_maxNumberOfScalarExpressions];
-  Matrix m_matrixExpressions[k_maxNumberOfMatrixExpressions];
+  /* Matrix has to be uninitialized by default which forces them to be
+   * Expression. */
+  Expression m_matrixExpressions[k_maxNumberOfMatrixExpressions];
   /* Matrix layout memoization */
   LayoutRef m_matrixLayouts[k_maxNumberOfMatrixExpressions];
 };
diff --git a/poincare/src/global_context.cpp b/poincare/src/global_context.cpp
index 6388272c1..536e36fe5 100644
--- a/poincare/src/global_context.cpp
+++ b/poincare/src/global_context.cpp
@@ -64,11 +64,13 @@ void GlobalContext::setExpressionForSymbolName(const Expression & expression, co
     int indexMatrix = symbol.name() - (char)Symbol::SpecialSymbols::M0;
     assert(indexMatrix >= 0 && indexMatrix < k_maxNumberOfMatrixExpressions);
     Expression evaluation = expression.isUninitialized() ? Expression() : expression.approximate<double>(context, Preferences::sharedPreferences()->angleUnit(), Preferences::sharedPreferences()->complexFormat()); // evaluate before deleting anything (to be able to evaluate M1+2->M1)
+    // Reinitialize the matrix layout
+    m_matrixLayouts[indexMatrix] = LayoutReference();
     if (!evaluation.isUninitialized()) {
       if (evaluation.type() != ExpressionNode::Type::Matrix) {
         m_matrixExpressions[indexMatrix] = Matrix(evaluation);
       } else {
-        m_matrixExpressions[indexMatrix] = static_cast<Matrix>(evaluation);
+        m_matrixExpressions[indexMatrix] = evaluation;
       }
     }
     return;
diff --git a/poincare/src/grid_layout_node.cpp b/poincare/src/grid_layout_node.cpp
index b9d2763f8..9f50cecbf 100644
--- a/poincare/src/grid_layout_node.cpp
+++ b/poincare/src/grid_layout_node.cpp
@@ -91,7 +91,8 @@ void GridLayoutNode::moveCursorDown(LayoutCursor * cursor, bool * shouldRecomput
 }
 
 void GridLayoutNode::didAddChildAtIndex(int newNumberOfChildren) {
-  GridLayoutRef(this).setDimensions(1, newNumberOfChildren);
+  setNumberOfRows(1);
+  setNumberOfColumns(newNumberOfChildren);
 }
 
 // Protected
@@ -239,7 +240,7 @@ KDCoordinate GridLayoutNode::height() const {
   for (int i = 0; i < m_numberOfRows; i++) {
     totalHeight += rowHeight(i);
   }
-  totalHeight += (m_numberOfRows-1)*k_gridEntryMargin;
+  totalHeight += max((m_numberOfRows-1)*k_gridEntryMargin, 0);
   return totalHeight;
 }
 
@@ -256,7 +257,7 @@ KDCoordinate GridLayoutNode::width() const {
   for (int j = 0; j < m_numberOfColumns; j++) {
     totalWidth += columnWidth(j);
   }
-  totalWidth += (m_numberOfColumns-1)*k_gridEntryMargin;
+  totalWidth += max(0, (m_numberOfColumns-1)*k_gridEntryMargin);
   return totalWidth;
 }
 
diff --git a/poincare/src/matrix.cpp b/poincare/src/matrix.cpp
index eb5ffdf46..9f671533b 100644
--- a/poincare/src/matrix.cpp
+++ b/poincare/src/matrix.cpp
@@ -22,6 +22,7 @@ int MatrixNode::polynomialDegree(char symbolName) const {
 }
 
 LayoutRef MatrixNode::createLayout(Preferences::PrintFloatMode floatDisplayMode, int numberOfSignificantDigits) const {
+  assert(numberOfChildren() > 0);
   MatrixLayoutRef layout;
   for (int i = 0; i < numberOfChildren(); i++) {
     layout.addChildAtIndex(childAtIndex(i)->createLayout(floatDisplayMode, numberOfSignificantDigits), i, i, nullptr);
@@ -89,6 +90,7 @@ Evaluation<T> MatrixNode::templatedApproximate(Context& context, Preferences::An
 // MATRIX
 
 void Matrix::setDimensions(int rows, int columns) {
+  assert(rows * columns == numberOfChildren());
   setNumberOfRows(rows);
   setNumberOfColumns(columns);
 }
diff --git a/poincare/src/symbol.cpp b/poincare/src/symbol.cpp
index 527e457d7..4aa4e3663 100644
--- a/poincare/src/symbol.cpp
+++ b/poincare/src/symbol.cpp
@@ -323,7 +323,7 @@ int Symbol::getPolynomialCoefficients(char symbolName, Expression coefficients[]
     coefficients[1] = Rational(1);
     return 1;
   }
-  coefficients[0] = Symbol(name());
+  coefficients[0] = clone();
   return 0;
 }