How unique are waypoint names supposed to be? I had thought that someone such as ICAO was coordinating the assignment of five-letter waypoint names such that they were globally unique.

Now I notice that OpenNav knows three different waypoints named PINTO, two of which are on the same continent.

Is this supposed to happen? Are there rules for how close identically-named waypoints can be to each other?

(A significant factor in the AA 965 crash was that there were two NDBs with the same ID close to each other, and the FMC selected the wrong one to fly towards. This might be inevitable when NDBs usually have one- or two-letter IDs, but surely with a big fat five-letter namespace uniqueness ought to be achievable?)
The names are not globally unique and when entering the plan into the FMC, the crew should check the leg distance.  They are sufficiently far enough that the crew will see 1,812 miles instead of 135 miles. 

Many FMCs will also only offer "sensible" choices and a deliberate action is required to select a "nonsensical" waypoint.

Often, a mistake in choosing the wrong waypoint will also alert them with a "not enough fuel" message, or an obvious gross error such as a total distance of 3,323 miles instead of the 756 miles expected.