GoneWest
My entry through MCO was a repeat trip which arose through a requirement to return to the U.K. for a couple of weeks following some training in Miami . I'm not entirely sure that an M1 was strictly correct as I wasn't really a student , however this was the visa that was issued ( organised by my employer ) , & at the time I was really none the wiser . I'm also not sure that a visa of this type is geographically sensitive but the INS officer was insistant that the visa waiver was the appropriate protocol on this occasion .
You mention ' loophole ' in your post ; I would suggest that moreover my case was nothing less than ignorant deception on the grounds that I really ought to have had a higher level visa & had completed my dealings with the Miami operation , hence had no reason to return using the M1 . I genuinely knew no better having taken the best advice I had from my company , but really it was no better than misleading the INS by claiming to be on vacation . I told the truth though , & the result was , perhaps , testament to my honesty ( again , all be it ignorantly ) .
I would like to reiterate the point made by yourself & others here : Do not jeopardise your unrestricted passport category by attempting to enter the U.S. without the correct paperwork - if your passport is endorsed with a refused entry stamp , it may at best limit your visits to the U.S. for recreation & possibly restrict your future employment with an airline .