I am drawing with a brush, using either an Intuos or a Cintiq. Once I have completed one stroke, I lift the pen, place it in a new position, to begin the next stroke. A glitch mistakenly joins the last stroke and the new one wiith a straight line which appears as soon as I start the new line. This happens wether I am using constrained (option key) stroke or not. Why am I having this problem?