diff --git a/poincare/src/expression_node.cpp b/poincare/src/expression_node.cpp
index b1399f073..66ba5d07e 100644
--- a/poincare/src/expression_node.cpp
+++ b/poincare/src/expression_node.cpp
@@ -12,8 +12,14 @@ TreeNode * ExpressionNode::FailedAllocationStaticNode() {
 
 ExpressionReference ExpressionNode::replaceSymbolWithExpression(char symbol, ExpressionReference expression) {
   ExpressionReference reference(this);
-  for (int i = 0; i < reference.numberOfChildren(); i++) {
-    reference.replaceTreeChildAtIndex(i, reference.childAtIndex(i).node()->replaceSymbolWithExpression(symbol, expression));
+  int nbChildren = reference.numberOfChildren();
+  for (int i = 0; i < nbChildren; i++) {
+    ExpressionReference newChild = reference.childAtIndex(i).node()->replaceSymbolWithExpression(symbol, expression);
+    if (reference.numberOfChildren() < nbChildren) {
+      reference.addChildTreeAtIndex(newChild, i, nbChildren - 1);
+    } else {
+      reference.replaceTreeChildAtIndex(i, newChild);
+    }
   }
   return reference;
 }
diff --git a/poincare/src/expression_reference.cpp b/poincare/src/expression_reference.cpp
index 4b09b17af..6af3a826d 100644
--- a/poincare/src/expression_reference.cpp
+++ b/poincare/src/expression_reference.cpp
@@ -107,7 +107,7 @@ bool ExpressionReference::getLinearCoefficients(char * variables, ExpressionRefe
     }
     x++;
   }
-  ExpressionReference equation = *this;
+  ExpressionReference equation = clone();
   x = variables;
   int index = 0;
   ExpressionReference polynomialCoefficients[k_maxNumberOfPolynomialCoefficients];
@@ -198,16 +198,28 @@ void ExpressionReference::Simplify(ExpressionReference * expressionAddress, Cont
 }
 
 ExpressionReference ExpressionReference::deepReduce(Context & context, Preferences::AngleUnit angleUnit) {
-  for (int i = 0; i < this->numberOfChildren(); i++) {
-    replaceTreeChildAtIndex(i, childAtIndex(i).deepReduce(context, angleUnit));
+  int nbChildren = this->numberOfChildren();
+  for (int i = 0; i < nbChildren; i++) {
+    ExpressionReference reducedChild = childAtIndex(i).deepReduce(context, angleUnit);
+    if (numberOfChildren() < nbChildren) {
+      addChildTreeAtIndex(reducedChild, i, nbChildren-1);
+    } else {
+      replaceTreeChildAtIndex(i, reducedChild);
+    }
   }
   return shallowReduce(context, angleUnit);
 }
 
 ExpressionReference ExpressionReference::deepBeautify(Context & context, Preferences::AngleUnit angleUnit) {
   ExpressionReference beautifiedExpression = shallowBeautify(context, angleUnit);
-  for (int i = 0; i < beautifiedExpression.numberOfChildren(); i++) {
-    beautifiedExpression.replaceTreeChildAtIndex(i, beautifiedExpression.childAtIndex(i).deepBeautify(context, angleUnit));
+  int nbChildren = beautifiedExpression.numberOfChildren();
+  for (int i = 0; i < nbChildren; i++) {
+    ExpressionReference beautifiedChild = beautifiedExpression.childAtIndex(i).deepBeautify(context, angleUnit);
+    if (beautifiedExpression.numberOfChildren() < nbChildren) {
+      beautifiedExpression.addChildTreeAtIndex(beautifiedChild, i, nbChildren-1);
+    } else {
+      beautifiedExpression.replaceTreeChildAtIndex(i, beautifiedChild);
+    }
   }
   return beautifiedExpression;
 }
diff --git a/poincare/src/rational.cpp b/poincare/src/rational.cpp
index fca5c59a6..b394678ec 100644
--- a/poincare/src/rational.cpp
+++ b/poincare/src/rational.cpp
@@ -127,11 +127,12 @@ int RationalNode::simplificationOrderSameType(const ExpressionNode * e, bool can
 // Simplification
 
 ExpressionReference RationalNode::shallowBeautify(Context & context, Preferences::AngleUnit angleUnit) {
+  ExpressionReference reference(this);
   if (m_negative) {
     m_negative = false;
-    return OppositeReference(ExpressionReference(this));
+    return OppositeReference(reference);
   }
-  return ExpressionReference(this);
+  return reference;
 }
 
 ExpressionReference RationalNode::cloneDenominator(Context & context, Preferences::AngleUnit angleUnit) const {