I'm writing on a GUI in Python/Tk - I have a subscriber which is  
listening for image messages and setting a class member variable with  
the newest image, and a GUI element that needs to use image (after  
sending a message to move a pan/tilt). On click I use rospy.sleep() to  
wait for the pan/tilt to settle down before using any images. However,  
I've noticed that once I call rospy.sleep() inside the click callback,  
the callback for the image subscriber stops getting called. It was my  
understanding that subscriber callbacks are run asynchronously in  
their own thread, so a sleep in a different thread should have no  
effect. What's going on here? What am I missing?

Thanks,
-Dan