1) Building my first long conveyor line, I built a conveyor pole where I was headed, and accidentally built the conveyor from the pole back to the line I was extending from the source. So I ended up with the new belt running opposite the old one >>><<<
Clicking around, I then managed to extend the belt as I originally intended, without deleting the opposite belt, and looped it back on itself:
2) After attempting to place a splitter right up against the output of a smelter (https://questions.satisfactorygame.com/1104/placing-splitter-attached-to-smelter-can-look-odd), and removing it - I noticed an iron ingot on the belt moving opposite all of the actual output:
3) After moving the splitter in #2 out further, deleting the belt between it and the next constructor, then attempting to re-place the same output belt, I got a "too steep" error. Even though it's the same path the belt was taking before the smelter was placed!