Strange Behavior Using Magnetic Lasso

Question

I'm using Photoshop CS4, and experiencing odd behavior when using the Magnetic Lasso. I'm working on a project that has fairly intricate outlining and filling actions, so I'm using the magnetic lasso to do that.  This involves a lot of irregular borders, so I have to do a fair amount of setting anchor points manually.  It all works fine, except that I periodically get the lasso "closing" spontaneously.  That is, I'll be half way around an area I'm outlining, and with no action on my part, the lasso suddenly leaps to the origin point (the pointer doesn't move, but the seleted area is completed, as if I had double clicked.  This seems to happen more frequently if I am moving the mouse back and forth to get a more precise location for setting an anchor point.  Does anyone have any idea what might be causing this behavior?  Sometimes, depending on where I am in the process, I can simply continue by choosing to "add to the selection."  But sometimes, this aribitrary closing encompases portions that I do NOT want included in the selection, so I have no choice but to Step Backwards, or Undo, and start over.  If it helps, when this happens, I'm usually working on a magnified portion of the image, and have the Caps Lock pressed to give me the pointer configured as a cross within a circle, to provide more precision.  Will be glad to provide any additional information that anyone considers helpful or pertinent.  Any help much appreciated.

Answer 1

Acidclink--
Thanks for the reply. And let me say at the outset that I am NOT an experienced Photoshop user.  I've used it a lot, but not much for many different projects.  Until I got your suggestion, I hadn't heard the term "penning a path." But I did some reading, and I'm assuming that you are talking about using the pen tool in its path mode, to draw an irregular outline that you can then convert into a selection.  Truth is, until your note, I had no idea that the pen tool could even be used in this manner.  And I will certainly give it a try.  But, as I understand it, the pen tool when used in this fashion creates a series of straight lines between points.  That would mean, (if I am correct) that to make a curved line, you would need a lot of points close together.  And in that situation, it seems to me that the Magnetic Lasso (or the Quick Selection) tool might work better.
Perhaps if I describe in a bit more detail what I am doing, it might help you and others who are generously trying to assist.  I'm working with a series of state outline maps with counties outlined.  Although the images are color images, they are essentially black and white.  That is, I have a map of a state on a white background, with the counties of the state outlined in black.  My task is to fill a single county on the map with color.  So what I've been doing is using the Magntic Lasso (or the Quick Selection) tool to outline the county boundary, then use the FILL command to fill the selection with the color.  As you can imagine, the county boundaries are often very irregular, with zig-zags, curves, rivers, etc.  The benefit of the magnetic lasso or quick selection tool is that they do a FAIR job of following all of the irregular coutours.  They ceratinly aren't perfect, and I nearly always have to add to or subtract from the selection to get a good quality selection that matches the preprinted boundaries.  But, what I don't have to do is trace the entire distance of the existing boudary with precision.  I just need to nudge the selection a bit in sharp pointed corners, or things like river meanders, where there are a series of "s" turns.
Having said all of that, I'm still willing to learn, and I do plan to try the pen tool to create a path as you suggest.  An earlier suggestion to use the Quick Selection tool has helped me--I've been using it to grossly select an area, then using the magnetic lasso to refine the seletion.  So I am learning (though slowly).  And I DEFINITELY appreciate the input and suggestions.
On a different subject, I MAY have fixed the unexpected closing problem with the magnetic lasso.  Since I unplugged the mouse (to try a different one which turned out to be dead), and plugged it back in again, I have not yet experienced the spontaneous closing problem.  So it may be that the problem was caused by a poor connection of the mouse to the USB port.  Time will tell on that.