I notice now that there are a lot of weird notification issues now. I ran some tests and this is what I've found.
Screen On - Clear all apps with Task Manager. Exit to home screen. Meaning, WhatsApp is not running in the background, not running at all. I use my girlfriends phone to send me 10 + messages. I get NO pushed messages, no notifications. Nothing happens. I then launch the app and see that I have 10+ unread messages under her name. I click to read the messages, and exit back to the home screen (either back arrow or home button). I send another message from her phone, and NOW I see the notifications.
Screen Off - (sleeping but app is still in the background) - I send a message from her phone, get NO push notification. But... as soon as I hit the power button to light up the screen (wake from sleep), I get the notification in the bar. I read the message, clear the notification bar.. then put the phone back to sleep. Same thing happens. While the screen is off, I get no push notifications until I turn on the screen.
Anyone having weird issues with WhatsApp? It can't be the app because it works perfectly normal on my Samsung Note. I'm thinking ICS broke it some how.