[pct-l] SoBo Border?

[Spring]

According to the PCTA "Trail Dirt" news "U.S. Customs and Border Protection no longer allows hikers and horseback riders to cross the international border from Canada into the United States"  They go on to state that hikers were fined (imprisoned) for violating this rule.  
 
Anyone have experience with this?  
 
And, how do they (the border guards)  know if you came from Canada or walked up from Highway 20, and are just on the return?  Do they now maintain patrols on the section south of the border?
 
Thanks, Spring