For WinForms, when autopanning, if the Origin has already been set, a mouse up just stops this tool. When manually panning, a mouse up just stops this tool, unless Modal is true, in which case this tool waits for a mouse down again to start panning during mouse moves.

For WebForms, the behavior is different. When autopanning, this method always sets the Origin to the FirstInput.ViewPoint, scrolls the view according to GoView.ComputeAutoPanDocPosition, and then stops this tool. When manually panning, this changes the GoView.DocPosition according to the difference between the mouse down and the mouse up points. Again, the value of Modal determines whether this tool then stops, or if it waits for another mouse down/up.

Reference

GoToolPanning Class
GoToolPanning Members