Index: trunk/src/obj_arc.c
===================================================================
--- trunk/src/obj_arc.c	(revision 29722)
+++ trunk/src/obj_arc.c	(revision 29723)
@@ -380,7 +380,7 @@
 static const char core_arc_cookie[] = "core-arc";
 
 typedef struct {
-	pcb_arc_t *arc;
+	pcb_arc_t *arc; /* it is safe to save the object pointer because it is persistent (through the removed object list) */
 	pcb_coord_t Thickness, Clearance;
 	pcb_coord_t Width, Height;
 	pcb_coord_t X, Y;
Index: trunk/src/obj_line.c
===================================================================
--- trunk/src/obj_line.c	(revision 29722)
+++ trunk/src/obj_line.c	(revision 29723)
@@ -120,7 +120,7 @@
 static const char core_line_cookie[] = "core-line";
 
 typedef struct {
-	pcb_line_t *line;
+	pcb_line_t *line; /* it is safe to save the object pointer because it is persistent (through the removed object list) */
 	pcb_coord_t Thickness, Clearance;
 	pcb_point_t Point1, Point2;
 } undo_line_geo_t;