Index: trunk/src/hid_cam.c
===================================================================
--- trunk/src/hid_cam.c	(revision 23521)
+++ trunk/src/hid_cam.c	(revision 23522)
@@ -434,6 +434,10 @@
 int pcb_cam_end(pcb_cam_t *dst)
 {
 	free(dst->inst);
+	if (dst->fn_template != NULL) {
+		free(dst->fn);
+		free(dst->fn_last);
+	}
 	dst->inst = NULL;
 	if (!dst->active)
 		return -1;
@@ -475,6 +479,13 @@
 	ctx.grp = pcb_get_layergrp(cam->pcb, gid);
 	ctx.vl = vl;
 	cam->fn = pcb_strdup_subst(cam->fn_template, cam_update_name_cb, &ctx, PCB_SUBST_HOME | PCB_SUBST_PERCENT | PCB_SUBST_CONF);
+	if ((cam->fn_last == NULL) || (strcmp(cam->fn, cam->fn_last) != 0)) {
+		cam->fn_changed = 1;
+		free(cam->fn_last);
+		cam->fn_last = pcb_strdup(cam->fn);
+	}
+	else
+		cam->fn_changed = 0;
 	return 1;
 }
 
Index: trunk/src/hid_cam.h
===================================================================
--- trunk/src/hid_cam.h	(revision 23521)
+++ trunk/src/hid_cam.h	(revision 23522)
@@ -8,6 +8,7 @@
 typedef struct pcb_cam_s {
 	/* public */
 	char *fn;
+	pcb_bool fn_changed;           /* true if last call changed the ->fn field */
 	pcb_bool active;
 	int grp_vis[PCB_MAX_LAYERGRP]; /* whether a real layer group should be rendered */
 	int vgrp_vis[PCB_VLY_end];     /* whether a virtual layer group should be rendered */
@@ -19,6 +20,7 @@
 
 	/* private/internal/cache */
 	const char *fn_template;
+	char *fn_last;
 	char *inst;
 	pcb_board_t *pcb;
 	int orig_vis[PCB_MAX_LAYER]; /* backup of the original layer visibility */