Jon, this is what I had mentioned a couple nights ago. Same thing for me
both on win32 and Linux. Only the first click on the button is obeyed
(while still hovering on that button)... then if you move the cursor off
the button and back on, you can click it one time again... so if you
want to move a layer downward 4 steps in the stack, you have to leave
the button 3 times to accomplish it.