Hello GlennT
Have just re-read your post, and it says that you Left Click and then move the curser to the window, whereas the normal way is to move the mouse curser until the 2 arrows appear and then click and hold the left mouse button, not releasing the button until you have moved the border to the new position. Are you sure you have not got them mixed up.
Another item to have a look at in the program you are using is to see if there is an option that when selected prevents the Windows from being re-sized.
Hope this helps

Bill