On click-release for Manipulator handles, without moving mouse, it will

stick to transform() until another mouse press (or ESC etc)

source/blender/src/transform.c

@@ -572,7 +572,7 @@ void Transform(int mode, int context)
 
 void ManipulatorTransform(int mode) 
 {
-	int ret_val = 0;
+	int ret_val = 0, mouse_moved = 0;
 	short pmval[2] = {0, 0}, mval[2], val;
 	unsigned short event;
 
@@ -648,6 +648,10 @@ void ManipulatorTransform(int mode)
 			event= extern_qread(&val);
 
 			switch (event){
+			case MOUSEX:
+			case MOUSEY:
+				mouse_moved = 1;
+				break;
 			/* enforce redraw of transform when modifiers are used */
 			case LEFTCTRLKEY:
 			case RIGHTCTRLKEY:
@@ -669,6 +673,8 @@ void ManipulatorTransform(int mode)
 				ret_val = TRANS_CANCEL;
 				break;
 			case LEFTMOUSE:
+				if(mouse_moved==0 && val==0) break;
+				// else we pass on event to next, which cancels
 			case SPACEKEY:
 			case PADENTER:
 			case RETKEY:

source/blender/src/transform_manipulator.c

@@ -162,7 +162,7 @@ static void stats_pose(ListBase *lb, float *normal, float *plane)
 
 /* centroid, boundbox, of selection */
 /* returns total items selected */
-static int calc_manipulator(ScrArea *sa)
+int calc_manipulator_stats(ScrArea *sa)
 {
 	extern ListBase editNurb;
 	View3D *v3d= sa->spacedata.first;
@@ -1318,7 +1318,7 @@ void BIF_draw_manipulator(ScrArea *sa)
 	if(G.moving==0) {
 		v3d->twflag &= ~V3D_DRAW_MANIPULATOR;
 		
-		totsel= calc_manipulator(sa);
+		totsel= calc_manipulator_stats(sa);
 		if(totsel==0) return;
 		
 		v3d->twflag |= V3D_DRAW_MANIPULATOR;