The Polygon Lasso Tool Closes Automatically

This tool is really starting to drive me up the wall.  If I'm going around a large image, being careful to use the tool, it will close automatically at seemingly random times.  Once this start happening, lines are crisscrossed and it becomes nearly impossible to salvage what you've already selected.

To make matters worse, adding new sections using the same tool it very flaky.  9 out of 10 times when I click to add the beginning of a new selection, no anchor is placed. down.  I end up clicking all around the image trying to get one started.