Please read the first comment. This is known bug in Ae, there are few ideas how to get around it
Tuesday 19 March, 2013 01:57:21
I have tried your technique for this tutorial, however when pasting the text to complete the 1000px x 1000px composition it allows me to fill about half of the composition with text and as soon as I paste another set of text all of it disappears. Any ideas????
Using this method is not possible. In order to assemble an image using a still image or video it's recommended to use a plugin like Trapcdoe Form. There's a third tutorial here which explains how to achive this. Instead composition of literature you'll need to put together a composition consisting of stills, The duration of each should be a single frame and all must be the same size.