AP Stylebook says NEVER use the colloquial term pled. So you will see "pleaded" in newspapers, but often "pled" is used in magazines and everyday conversation. Neither is wrong, either is right. When I receive a court document saying someone "pled", I change it to "pleaded" when writing a news article. For the court reporter, pled is correct. For the newspaper writer it is not. The term plea is a legal term in these instances meaning simply an answer to a claim made by someone in a civil or criminal case under common law using the adversary system, and as such should not be confused with common language definition of the word, such as beg.
As in many words, the American English language has ignored logic. However, I join my colleagues above who cringe at some of the current generation's colloquialism.