I went through a period of thinking the same: sometimes it would seem to want to type a letter instead of triggering the cursor movement. I think the key is tha

I went through a period of thinking the same: sometimes it would seem to want to type a letter instead of triggering the cursor movement. I think the key is that you just keep your finger on the screen while applying a bit more pressure (press harder, then release the pressure without lifting off the screen) to trigger the trackpad mode. I now find it 100% reliable and can't figure out how to trigger the odd behaviour I was previously experiencing.