Pen tool line automatically continues after anchor point

Hi,

Typically with the pen tool I would click to create my first anchor point. Then click elsewhere to create a second anchor point, after doing so a line is created.

I jumped on another computer recently and it didn't behave this way.

Instead I clicked to create the first anchor point and then as a dragged the mouse over to position to the second anchor point a line was being created automatically with the mouse as if the line was sticky to wherever the cursor went. The only way to break this was to move the mouse over the line already created and add a third anchor point in the middle of the line. I didn't try to reset the tool at the time, just got on with it.

How has the pen tool got into this state and how is it undone without simply resetting the tool?

Thanks in advance.