I think it might be that some interaction with Sitrus Berry got confused with the entire ability. If I`m understanding right, it might be that Sitrus Berry activates and heals Golisopod so his ability won`t trigger in that instance but I haven`t tested this. I`m testing ingame whether Leech Life also allows you to reuse EE like ZParting Shot does, cause the rumor that if Golisopod heals back up it won`t trigger must have started from something, right?
Edit: Leech Life also works...so I`m lost on how the rumor that if you heal over 50% after using EE once it won`t happen again began. I won`t try the Sitrus Berry approach because that seems unrealistic, I don`t think anyone would actually use that instead of everything else available. Still, feel free to try it out. I`m going to sleep and when I wake I might test if Leftovers also work, just trying to debunk as many rumors as possible (though if someone else wants to do it, feel free. Less work for me XD).
PS: ZParting Shot ignores Taunt, so you can`t be stopped from healing someone unless killed before you do so. Just something to have in mind if you decide to pair Golisopod with a ZPS user.