On Android 4.0 devices (or maybe just tablets? haven't nailed this down yet) the widget displays the app icon and + button, but no tasks.
My experience of this is on an LG V900 tablet running Android 3.1 and a Dell Streak 5 running a 2.3.3 DSC ROM. On both devices the widget's tasks are displayed in portrait but not landscape mode. Is anyone with any other devices/android versions seeing this to help find out which devices and versions it's applicable to?
Actually, I'm having this issue too. I thought it was due to the unstable ROM I was running, but I've since changed ROMs and it still isn't working (both are Gingerbread, for what it's worth, and this is on a phone). The tasks show up when I first create the widget, but eventually they'll go away and the widget will just say "No tasks to display", even if the app has lots of tasks in it.
I have the same problem on my Acer Iconia Tab A500 tablet running Android 4.0. In portrait mode it shows the top three tasks. The icon and plus are shown on the right hand side of the widget. However, when I hold it in landscape mode the Todo.txt Touch widget only shows the icon and plus at the left hand side. It doesn't show any tasks.