It seems maddeningly random. I want to create a guide line that is perpendicular to the direction of the cursor, or straight in line with the movement of the cursor. I was hoping that simply using the ctrl key to add a plus sign next to the cursor would select for one or the other but it seems to do nothing.
I’m sorry that I have not yet learned how to upload a vid of the behavior. I hope that I’ve described it in sufficient detail.