Index: src/app/qgssinglesymboldialog.h
===================================================================
--- src/app/qgssinglesymboldialog.h	(revision: 11107)
+++ src/app/qgssinglesymboldialog.h	(copia de trabajo)
@@ -74,6 +74,7 @@
     /** Default constructor is private, do not use this */
     QgsSingleSymbolDialog();
     QString mTexturePath;
+    bool isEqual( double x, double y );

   signals:
     void settingsChanged();
Index: src/app/qgssinglesymboldialog.cpp
===================================================================
--- src/app/qgssinglesymboldialog.cpp	(revision: 11107)
+++ src/app/qgssinglesymboldialog.cpp	(copia de trabajo)
@@ -31,6 +31,8 @@
 #include <QImage>
 #include <QFileDialog>
 #include <QListWidgetItem>
+#include <cmath>

 #define DO_NOT_USE_STR "<off>"

@@ -439,7 +441,7 @@
   if ( lstSymbols->isEnabled() && lstSymbols->currentItem()->data( Qt::UserRole ).toString() != sy->pointSymbolName() )
     lstSymbols->setEnabled( false );

-  if ( mPointSizeSpinBox->isEnabled() && mPointSizeSpinBox->value() != sy->pointSize() )
+  if ( mPointSizeSpinBox->isEnabled() && !isEqual( mPointSizeSpinBox->value(), sy->pointSize() ) )
     mPointSizeSpinBox->setEnabled( false );

   if ( mRotationClassificationComboBox->isEnabled() &&
@@ -450,7 +452,7 @@
        mScaleClassificationComboBox->itemData( mScaleClassificationComboBox->currentIndex() ).toInt() != sy->scaleClassificationField() )
     mScaleClassificationComboBox->setEnabled( false );

-  if ( outlinewidthspinbox->isEnabled() && outlinewidthspinbox->value() != sy->pen().widthF() )
+  if ( outlinewidthspinbox->isEnabled() && !isEqual( outlinewidthspinbox->value(), sy->pen().widthF() ) )
     outlinewidthspinbox->setEnabled( false );

   if ( btnFillColor->isEnabled() &&  btnFillColor->color() != sy->brush().color() )
@@ -591,3 +593,7 @@

 }

+bool QgsSingleSymbolDialog::isEqual( double x, double y )
+{
+    return std::fabs( x - y ) <= 0.0001;
+}
\ No newline at end of file