A colleague of mine, pointed this out to me today and it is a rather serious bug with the Lasso Tool. Select the Lasso Tool from the Tool Pallette in either Flash MX or Flash MX 2004.
Then in the options panel at the bottom of the Tool Pallette, select Polygon Mode.
Now click a few times around the screen to add to your selection outline, then press and hold the space bar and move your mouse which will move the stage around. All of this thus far is expected behaviour. Now let go of the space bar and this is where it starts to go wrong, the cursor isnt changed back to the Lasso and now when you click around the stage the lines and start points are all messed up. To get out of this bug, you will have to right click twice.