Trying to explain the video a little better: Once you click and drag with an underground, it locks the line in which further undergrounds will be placed. However, it will not actually place them unless the cursor is located directly on that line. If your cursor drifts off the set line, you can get far away from the last-placed underground, and they all get built suddenly when you move the cursor back onto the set line.
Expected behavior is for undergrounds to continue being built along the set line as you drag the cursor in X, ignoring any drift in the Y direction away from the line.
when i click to build a belt in a line it does fun. i release the mouse button and press it again and go a different direction then it is still stuck in that direction(unless i wait a few seconds). is this intentional? is there a way to change this. it would be nice if the belt moved in the direction of the drag right away