Index: Classes/Persistence/Backend.php
===================================================================
--- Classes/Persistence/Backend.php	(Revision 2531)
+++ Classes/Persistence/Backend.php	(Arbeitskopie)
@@ -523,12 +523,9 @@
 			}
 		}
 
-		if ($columnMap->getTypeOfRelation() === Tx_Extbase_Persistence_Mapper_ColumnMap::RELATION_HAS_AND_BELONGS_TO_MANY) {
-			$this->deleteAllRelationsFromRelationtable($parentObject, $propertyName);
-		}
-
 		$currentUids = array();
 		$sortingPosition = 1;
+		$cleanPropertyValue = $parentObject->_getCleanProperty($propertyName);
 		foreach ($objectStorage as $object) {
 			if ($object->_isNew()) {
 				if ($object instanceof Tx_Extbase_DomainObject_AbstractEntity) {
@@ -537,18 +534,21 @@
 					$this->persistValueObject($object, $sortingPosition);
 				}
 			}
+				// object newly added to the relation
+			if (!$cleanPropertyValue->contains($object)) {
+				$this->attachObjectToParentObject($object, $parentObject, $propertyName, $sortingPosition);
+			}
 			$currentUids[] = $object->getUid();
-			$this->attachObjectToParentObject($object, $parentObject, $propertyName, $sortingPosition);
 			$sortingPosition++;
 		}
-		
+
 		if ($columnMap->getParentKeyFieldName() === NULL) {
 			$row[$columnMap->getColumnName()] = implode(',', $currentUids);
 		} else {
 			$row[$columnMap->getColumnName()] = $this->dataMapper->countRelated($parentObject, $propertyName);
 		}
 	}
-	
+
 	/**
 	 * Returns the current field value of the given object property from the storage backend.
 	 *