In conformance with the IEC 61000-4-2 ESD test method, if the unit under test, such as a typical battery operated portable, does not have a ground return, a probe with in series to the ground return will be used to bleed off stored charges from accessible contacts between discharges.
What exactly happen at UUT when the stored charge is bleed off? UUT will only exhibit display problem at the moment of bleeding off the stored charge. No display related problem was seen, if the UUT was zapped without bleeding off the charge. But there is high possibility of seeing display problem when bleeding off the charge. Why?