fixed an issue pointed out by Tim

src/storm/builder/ExplicitModelBuilder.cpp

@@ -309,7 +309,7 @@ namespace storm {
             buildMatrices(transitionMatrixBuilder, rewardModelBuilders, choiceInformationBuilder, markovianStates);
             
             // Initialize the model components with the obtained information.
-            storm::storage::sparse::ModelComponents<ValueType, RewardModelType> modelComponents(transitionMatrixBuilder.build(), buildStateLabeling(), std::unordered_map<std::string, RewardModelType>(), !generator->isDiscreteTimeModel(), std::move(markovianStates));
+            storm::storage::sparse::ModelComponents<ValueType, RewardModelType> modelComponents(transitionMatrixBuilder.build(0, transitionMatrixBuilder.getLastRowGroup()), buildStateLabeling(), std::unordered_map<std::string, RewardModelType>(), !generator->isDiscreteTimeModel(), std::move(markovianStates));
                         
             // Now finalize all reward models.
             for (auto& rewardModelBuilder : rewardModelBuilders) {

src/storm/storage/SparseMatrix.cpp

@@ -272,6 +272,15 @@ namespace storm {
             return lastRow;
         }
 
+        template<typename ValueType>
+        typename SparseMatrixBuilder<ValueType>::index_type SparseMatrixBuilder<ValueType>::getLastRowGroup() const {
+            if (this->hasCustomRowGrouping) {
+                return currentRowGroup;
+            } else {
+                return getLastRow();
+            }
+        }
+
         template<typename ValueType>
         typename SparseMatrixBuilder<ValueType>::index_type SparseMatrixBuilder<ValueType>::getLastColumn() const {
             return lastColumn;

src/storm/storage/SparseMatrix.h

@@ -219,6 +219,13 @@ namespace storm {
              */
             index_type getLastRow() const;
 
+            /*!
+             * Retrieves the most recently used row group.
+             *
+             * @return The most recently used row group.
+             */
+            index_type getLastRowGroup() const;
+
             /*!
              * Retrieves the most recently used row.
              *