The new iPad is a lot like the old iPad, except when it comes to Smart Covers. Apparently some old Smart Covers and third-party cases aren't working with the new iPad. The reason? Polarity matters now.
The new iPad's Smart Cover wakeup is based on the polarity of the magnets. Problem is, older Smart Covers and cases were put together without regard for which way the magnet was facing. The issue was discovered by Mark Booth just after the new iPad launched, and has now been tested and confirmed by third party case makers. Some have offered replacements.