This was discussed in a forum post here
With this question type due in core for Moodle 3.0 more people will come across this usability issue. Since I posted that code I have some improvements that allow a completed shape to be moved with the mouse (Alt Click where you want the new center of the shape to be). I still don't have code to edit a shape once created as Tim suggested. However even with that limitation I believe code like this will will make the difference between many people giving up with the question type or actually using it.