xprop selects only the first window, when clicking on a tab-group of them.
solution is to go the hierarchy up to the topmost window. i put it all together
in a little package called akxprop but that was just for convinience for some
people to test it.

for those who are unaware of what tabs are: http://fluxbox.org/features/tabs.php

the whole thing comes down to:

+- patch ------------

--- dsimple.c	2004-12-22 15:08:49.847042792 +0100
+++ dsimple.c.new	2004-12-22 15:07:11.517991080 +0100
@@ -531,6 +531,17 @@ Window Select_Window(dpy)
       if (target_win == None) {
 	target_win = event.xbutton.subwindow; /* window selected */
 	if (target_win == None) target_win = root;
+      } else { /* search topmost window (for tab-supporting wm's) */
+		Window root_return;
+		Window win_return;
+		Window parent_return;
+		Window *children_return = NULL;
+		unsigned int nr_children = 0;
+		if (XQueryTree(dpy, target_win, &root_return, &parent_return,
+			&children_return, &nr_children)) {
+			target_win = children_return[nr_children - 1];
+			XFree(children_return);
+        }
       }
       buttons++;
       break;

+- end of patch -------------