There are 2 vars that control this, max_intro_words and max_intro_chars. If you are running the latest cvs version, then they should already be there, set them to 0 to disable the max size of the intro count. If you don't have those vars, and you just upgraded from cvs, then you need to add them in. They should just act disabled though if they aren't there.

So check to make sure those aren't to some really small value, and set them to 0 if you don't want a max size. It should give you an error telling you that you have exceeded the maximum size though, and tell you what it is.