Why is Lipulekh at centre of India-Nepal border dispute?

Nepal and India have had boundary dispute over Lipulekh, a pass located at tri-junction of India, Nepal and China. The main dispute concerns the location of the Kali River. Under 1816 Sugauli Treaty, Nepal ceded all territory west of the river. Nepal says Lipulekh lies east of the river and belongs to it, while India says it's part of Uttarakhand.