It's a general rule in web design that you should avoid making the user do
lots of scrolling, you are more likely to lose the users interest. That
said, a large document in a scrolling text box is a very poor design choice.
A large document should be a stand-alone web page. That said, depending on
the length you should break it up across more than one page, the user will
be more comfortable with clicking a continue link than with scrolling and
scrolling and scrolling some more.  I recommend you read
http://www.davidbartosik.com/arc/commonmistake.htm

As far as your actual issue, it appears that the code dialog has a character
limit. And you would be the first person I know of to have found it.

See first paragraph for a workaround.

at a certain point. Is there a size limit on the text in this scrollable
text area? Is there any way around it, or another suggestion for larger
documents?