Index: /trunk/qgis/src/app/qgsfieldcalculator.cpp
===================================================================
--- qgis-1.4.0/src/app/qgsfieldcalculator.cpp (revision 12551)
+++ /trunk/qgis/src/app/qgsfieldcalculator.cpp (revision 13046)
@@ -25,4 +25,9 @@
   setupUi( this );
 
+  if ( !vl )
+  {
+    return;
+  }
+
   populateFields();
   populateOutputFieldTypes();
@@ -32,5 +37,5 @@
   mOutputFieldPrecisionSpinBox->setValue( 3 );
 
-  mUpdateExistingFieldCheckBox->setCheckState( Qt::Checked );
+
 
   //disable ok button until there is text for output field and expression
@@ -40,7 +45,13 @@
   if ( !( vl->dataProvider()->capabilities() & QgsVectorDataProvider::AddAttributes ) )
   {
+    mUpdateExistingFieldCheckBox->setCheckState( Qt::Checked );
     mUpdateExistingFieldCheckBox->setEnabled( false ); // must stay checked
     mNewFieldGroupBox->setEnabled( false );
     mNewFieldGroupBox->setTitle( mNewFieldGroupBox->title() + tr( " (not supported by provider)" ) );
+  }
+
+  if ( vl->selectedFeaturesIds().size() > 0 )
+  {
+    mOnlyUpdateSelectedCheckBox->setChecked( true );
   }