Yes, some people use popcorn salt because it dissolves easier but if they have hard water or water with a lot of minerals in it, it will also cause streaking and sometimes the combination of both, makes it even worse. That is one of the reasons I use salted butter, so I don't have to worry about adding salt. One of those weird issues that comes up for some folks at some times. Funny thing, I never had any of these issues and then one day, instead of buying my Crisco in the tub like I usually do, I bought the 1 pound box. I ended up with the little white lumps which was the shortening not mixing in, in this case. I had found that for some reason, this box of Crisco was really dry, the shortening wasn't as creamy as usual so likely this is why it wouldn't mix in right. Anyway, haha, I finally knew the frustration, haha!
Hugs Squirrelly Cakes