Is there a limit on the amount of images/characters used in a post?
EDIT: There is a limit on the amount of textile code you use, so if you just use plain HTML you will avoid the limit and the post will still be shown correctly formatted.
The limit to textile formatting is much lower than the character limit (thousand-something characters in forums). You can still write once you exceed this limit, but the formatting is no longer working. You can use HTML coding, which requires a bit more typing but prevents the formatting from breaking.