Well, there are a lot of rules (including prescriptions and class rules) that can get you tossed for all sorts of reasons, and at higher levels of the sport (particularly qualifiers, international events and Olympics), you should almost expect to be protested if you do not follow them. For better or worse (depending on your perspective), it's all part of the game.
Now, in reading your posts John, I'm having difficulty understanding where in the prescription, or on the USSA PFD webpage, there was a clause that made the CE vest at that youth event legal enough to justify a warning and not a DSQ. Was there something else in the SIs that allowed the PC to issue a warning for this infraction? This was a US sailor on a US boat in US waters, right?
This is the sort of thing that could lead to an appeal at a minimum, up to everyone's new favorite buzzword, arbitration.
Please help me understand this a bit more in case I find myself on a PC for such a thing...