MackieStingray: I suppose it's of little consequence. I'd somehow never managed to figure out that Slappy can guide you to a cave with a supermutant and a deathclaw, so I'd only ever returned to Butch after killing off the Mother Deathclaw in the L.A. Boneyard. Now that I know better, I'm not sure I'll ever have reason to care about the scripting error again, much less have cause to see if this version fixed it.
GOG usually only provides game functionality and compatibility patches so I doubt it's fixed in vanilla GOG version. However there is unofficial patch available by TeamX that does fix number of scripting and other bugs in game. Unfortunately such fixes usually only work with new games or if you have never visited particular place. Also I did not find any mention of butch or harris in patch readme.
You can find the patch on
Petrell's Domain's downloads section inside fallout folder. Install "fallup121rc3.7z" first (it also uncensors the game and brings back the children if your version did not have them) and then "fallup13.7z" (the unofficial patch). Optionally you can also install "sfall1.7z" (middle mouse button and scroll wheel functionality) and f1npcmod.7z (if you use NPC companions). Read the readme's for specific installation instructions and more info about what each does.