Comment 18 for bug 1011073

(nm-applet:10742): GdkPixbuf-CRITICAL **: gdk_pixbuf_composite: assertion `dest_y >= 0 && dest_y + dest_height <= dest->height' failed

^^ That shouldn't be happening. It could be indicative of the cause of the issue though; in the case that you're using a custom icon set, maybe the pixbuf compositing, in the way it's done, causes some memory to be leaked. It should be apparently in the valgrind log, I'll take a look.

It would be useful if you could confirm what icon theme is in use though ;)