When a polymorphic search is performed HQLQueryPlan.performList() never return any results because there is a mistake in this code:

for ( int x = 0; x < size; x++ ) {
    final Object result = tmp.get( x );
    if ( distinction.add( result ) ) {
        continue;
    }
    includedCount++;
    if ( includedCount < first ) {
        continue;
    }
    combinedResults.add( result );
    if ( max >= 0 && includedCount > max ) {
        // break the outer loop !!!
        break translator_loop;
    }
}

The call to distinction.add( result ) returns true when the result is added and false when the result is already in the set. So the if code should be:

    if ( !distinction.add( result ) ) {
        continue;
    }