@Matthew: Except that pleaded is the both the prevailing usage and older than pled. It's not so much a new hack as commenters claim in this thread but both a throwback and signs of a lesser variant starting to lose even more ground.

Synesis doesn't really bother me, but I do edit it out of American texts especially when it's inconsistently applied. The usage is not, however, an error.

Yes, those are both proper American English as well. The first has a variant (pled, the subject of this thread) that is used in the States, but less often; the second, hanged, is utterly correct on both sides of the pond.

Quoting the 2009 edition of a preeminent reference called MODERN AMERICAN USAGE's entry titled PLEADED; PLED; PLEAD (which cites American sources for all those examples pronouncing it a colloquialism or slang), seems relevant to the topic at hand.

The use of "pled" in American English gained some ground circa the 1950s, but that form is both newer and lesser used in this country than the predominant "pleaded"; the claim that pleaded is either ungrammatical, newfangled, or incorrect has no basis. While pled is common enough, it is in fact the upstart and less used variant here in the States.

"Correct" and "proper" or even "prevailing American usage" are rather slim (if not false) defenses of pled. "Sounds funny," however, is a perfectly fine personal motivation.

Bryan Garner, quoted earlier, author of both Modern American Usage and editor of Black's Law Dictionary for over 20 years, is an excellent guide. Recapping somewhat, for those under the impression that pleaded is somehow newfangled when what they really mean is that the word sounds irksome to them:

"Traditionally speaking, pleaded is the best past-tense and past-participial form. Commentators on usage have long said so, pouring drops of vitriol onto 'has pled' and 'has plead':

[Then he cites usage books from 1893, 1905, 1906, 1926 "The past tense is pleaded. The use of pled or plead is colloquial", 1928, 1940, 1943. All of which fall rule pled as either wrong or slang.]

"The problem with these strong pronouncements . . . is that pled and plead have gained some standing in AmE, as noted in the 1950s: 'In the United States pleaded and pled are both acceptable. . . . In Great Britiain, only the form pleaded is used and pled is considered an Americanism.

"Indeed, pled . . . is nearly obsolete in BrE, except as a dialectical word. Nor is it considered quite standard in AmE . . . though it is a quite common variant. . . .

"Still, pleaded is the predominant form in both AmE and BrE and is always the best choice. . . ."

So, plead is a regular verb as of the 13th century, but 300 years later there was introduced the dialectical form and it was sometimes an irregular verb, which has lingered, dropped out of British English almost entirely, but gained a toehold in American English around the 1950s. Even so, it remains a lesser variant.