Contrary to claims that the original iPad Smart Cover (released alongside the iPad 2 in March 2011) doesn’t work or works inconsistently with the new iPad, we’ve tested both leather and plastic versions of that Smart Cover with multiple third-generation iPads, and both work reliably.
But iLounge observed that some Smart Covers did not work with the new iPad:
There was a quiet, unexplained update in the middle of last year to the Smart Cover, and it’s possible that different batches of Smart Covers were made inconsistently, but the original Smart Covers seem to be just fine.
According to iLounge, the reason for the problem could be due to the change in polarity of one of the sensors in the new iPad:
The issue has been traced to an iPad sensor that was reversed in polarity in the new model, causing some of the third-party magnet designs to fail—and possibly some of Apple’s, too.
They’ve also found that not all third-party cases work with the new iPad:
Results with third-party cases for the iPad 2 and new iPad are all across the board. They are so inconsistent, in fact, that we’ve tested a “third-generation iPad” case in multiple colors that vary in performance by color. The black and brown versions we received for testing work just fine. Gray and red versions don’t work at all. Other cases we’ve tested seem to work or not work without regard to colors, but manufacturing for many companies is not entirely perfect, and sometimes varies from batch to batch.
While case manufacturers seem to have acknowledged the issue and are willing to give a free replacement, we would strongly recommend you to hold off buying the magnetic Smart Cover like cases until there is more clarity or at least test the case with the new iPad before buying it.