If the video isn’t helpful enough or you can’t watch it:
When you try to apply a texture to a part, it behaves as expected and allows you to drag and drop textures on whatever face you want, (as intended I hope). However, once you union the part, (negate or not), the UV is completely wacked out and stretches the texture. The texture is like that forever until you separate the union and turn it back into a part. As well, you cannot drag and drop the texture on whatever face you want unlike a part.
Expected behavior
I expect that when I apply a texture to a union, the texture isn’t stretched to infinity. I also expect the drag and drop to work on any face you want for both parts and unions (only works with parts unlike before where it worked with both parts and unions).