Hi,
it happened to me that the counter of this challenge was increasing by itself, even if I was not disintegrating an enemy; so after some time i completed this challenge without having actually disintegrated 32 enemies with energy weapons. It said that the challenge was completed some time after having killed three bark scorpions in a Nipton house with a GRA plasma pistol and having quitted the house but i did not turn them into goo, so it should not count for the challenge. Is there an explanation of this? Thanks

So... has no one experienced this bug?

I haven't played NV in ages but this is from the wiki
Once you have disintegrated something or someone and you leave the area you are in, by entering another area or fast traveling away, upon your return you will be awarded again for the goo/ash piles left in that area. For example, if you create 4 goo piles and you leave the area with a challenge score of 4/32, when you come back to this area again, your score will increase to 8/32.