For all the DQ-trigger-happy folks, please give me the rule number under which a match DQ is warranted.
I fear that too many people in IPSC, especially recently minted officials, have a tendency to confuse their "gut reaction" or personal feelings with actual rules.
Unless you can find me a rule number which states that doing this is a DQ-able offence, you'd just embarras yourself by trying to DQ someone who manually loaded a round into the chamber.
As far as saying that this had the "potential" to cause a discharge, so what? So does manually decocking for the first shot, if you're not careful. If the gun remains pointed in a safe direction, you're fine, and if it doesn't, well, that THAT is something you can/will get DQed for.
Your job as officials is to enforce the rules, not expand on them. It is NOT your job to make the jumps from "bad idea" to DQ. Vince Pinto and his friends are always on a lookout for new ideas, feel free to submit it to them. Until it makes its way into the little red book, as long as you don't cause the gun to fire while doing it, it's perfectly legal.