Not sure if it intentional but there is a rule that I can only see in the Explorer rules.

That is that you can only fly a maximum of one flight that goes from a west coast to east coast airport (or the other way around). Of course you can still do multisegment flights to traverse the country but you use up segments quicker.

However I can see no mention of this in the Global Explorer so presumably to rack up miles you could do:

JFK-LAX-MIA-LAS

Julian