If ever you're typing in the wordpress app an iPhone notification message popsup (a text message alert or a calender alert) you're kind of screwed. What happens is that the notification alert takes priority and blocks you from using the wordpress app until you dismiss the popup. But the wordpress app keyboard blocks the buttons of the popup so you can't dismiss the popup.
You're forced to try and restart the app or even reboot the iPhone to clear this deadlock. Fortunately the app seems smart enough to recover your typing so you don't lose anything from the reboot. Potentially this is an iPhone OS design problem and not just limited to the wordpress app.