why gtol is not visible in the drawing tree?

I create a gtol with ProToolkit, the steps are as follows,

ProGtoldataAlloc(drawing,&gtd);

ProGtoldataTypeSet(gtd,type,&gtds);

ProGtoldataModelSet(gtd,solid,&gtds);

ProGtoldataReferenceSet(gtd,rtype,reference,&gtds);

ProGtoldataPlacementSet(gtd,ptype,NULL,NULL,location,NULL,&gtds);

ProGtoldataPlaneSet(gtd,&plane);

ProGtoldataGtoldatumrefSet(gtd,NULL,NULL,NULL,&gtds);

ProGtoldataDiameterSet(gtd,diameter,&gtds);

ProGtoldataValueSet(gtd,b_v,d_v,name,&gtds);

ProGtoldataMatCondSet(gtd,matcond,&gtds);

ProGtolCreate(gtd,&gtol);

ProGtoldataFree(&gtd);

ProDrawingtreeRefresh(drawing,PRO_VALUE_UNUSED);

the result is NO error, and the gtol is displayed on the drawing,

However, the gtol is not displayed in the drawing tree.

if i set the placement of the gtol (created by the protoolkit) as freenote once more in the drawing,(without any other change)

the gtol is visible in the drawing tree then.

Do i missed some statements, or set something wrong?

Look forward to your helps.