So I did a "reset all network connections" on my mini. Now the wifi connection is persistent and my push notifications - push/exchange mail, iMessage, etc., are working properly with the Smart Cover closed, even 10+ minutes after the screen has been turned off.
Hurray! Back to normal. That was odd. Never saw that bug before. Guess I have to keep the mini!
Hurray! Back to normal. That was odd. Never saw that bug before. Guess I have to keep the mini!