I recently set up a new TV/home theater system for my dad. The TV had 3 HDMI devices plugged into it. I plugged a 4th HDMI cable into the TV, and as I reached for the opposite end of the cable with the intent of plugging it into another HDMI device, I received a shock from the metal shield on the HDMI connector. This was not a brief static electricity shock--it was a sustained, AC shock that went up my hand into my wrist.
I investigated the outlet powering the TV and associated equipment (all plugged into the same surge strip), and I found that 1.) hot and neutral were reversed, and 2.) although the outlet had an earth ground prong, the house actually has no wiring for an earth ground (it's an old building). I replaced the outlet with a new GFCI outlet, correcting the hot/neutral reverse. After making this change, I found that the HDMI cable no longer shocks me.
I have found several posts around the internet discussing similar situations, and suggesting that a hot/neutral reverse is a common culprit. However, I am struggling to understand why exactly this wiring issue would lead to the HDMI cable shocking me. Most of the devices plugged into the power strip at the time of the shock (TV, cable box, AV receiver, etc.) were 2-prong, double-insulated devices. My understanding is that these devices do not "care" whether hot and neutral is reversed, and electrically isolate their shield/chassis from both hot and neutral. There was one device with a 3-prong plug (a computer) plugged into the surge strip (but not the TV) at the time of the shock, but I'm not sure whether that's relevant.
So, could someone please help explain: how does a hot/neutral reverse lead to mains voltage leaking into the HDMI shield of a double-insulated device?