It works well for both CvRTrees [[CvRTrees]] and CvSVM [[CvSVM]] for training regression function to generate xml files. But the program will crash if

CvRTrees [[CvRTrees]] obj;
obj.load(xml_file); //crash here

or

CvSVM [[CvSVM]] obj;
obj.load(xml_file); // crash here

Note: for classification, there is no such problem.