Sorry guys but I played with it some more and this may be helpful for those of you with weaker magnets in their non-Apple Smart Covers!
I really don't have a Smart Cover but a Miniot wood cover that functions just like a Smart Cover less the hinges. I've used this with my iPad 2 without issue and recently upgraded to the ipad 4 last Friday and just didn't start noticing until today that the iPad 4 does not lock/unlock when covered/uncovered as with my iPad 2. This is probably due to the added thickness....talk about margin of error!