I've made some new current draw measurements with my lab HP 20b. I was astonished to see that having HP's cable plugged in alone, even with the calculator turned off, draws permanently 5 mA. This is 20 times what the wp34s firmware draws in idle mode!
So unplug the cable when you're done with flashing!
BTW, I'm working on the power requirements of the wp34s. It will go down, at least in idle mode, be assured! :-)