Our border with Canada has had few problem locations that needed to be figured out (canada-united-state-borders-5-minute) including a major challenge in the San Juan Islands (borderlines-and-oregon-country-Whatcom). Point Roberts may have been overlooked during the initial border draw, but its value as access to salmon runs for Americans precluded any talk of a border adjustment. Issues associated with inaccuracies of the original 49th parallel survey were readily worked out.
A new border dispute arose in 1977 when nations began laying claim to coastal waters. Google Earth ends the U.S. - Canada boundary at the mouth of the Strait of Juan de Fuca.
The question beyond the entrance of the strait uses the same principle as within the strait. The line is drawn equidistant between the two shores. Hence, the border in the ocean takes trend line to the southwest beyond the strait. The dispute has to do with where one starts to draw the line from the coast. The Americans used the low water line off the northwest coast. The Canadians used as starting point a line drawn along the Vancouver Island shore from point to point.
From Gray (1997) (IBRU Boundary and Security Bulletin)
The differences between the two methods creates two small slivers of ocean water in dispute. The northeast sliver may be the more important one in that it includes the Swiftsure Bank. Swiftsure is touted by fishing charter folks on both sides of the border.