Operating System: Windows 7
I found that attacking a shocker zombie in one of the latest experimental versions would shock you invariably, if you engaged him in melee. I was even shocked for missing and dealing no damage whatsoever. I also receive damage when attacking with an insulating weapon (made from wood).
This is a considerable issue, since it makes dealing with shockers in melee unfairly dangerous and inconvenient.
To recreate the issue, simply play this version and attack a shocker zombie until you “miss”, and observe that you are still electrocuted. You can also attack him with a wooden item or otherwise non-conductive material, and see that it still invariably shocks you for every round of combat you engage in.