[3.5.3] Site sometimes imposing a word limit on chapters?

URL to your eFiction: http://chosentwofanfic.com
Version of eFiction: 3.5.3 I think
Have you bridged eFiction, if so with what?: Nope
Version of PHP: 5.4 is a recent upgrade, but this error occurred on 5.2 as well.
Version of MySQL: ...Not sure how to check this?
Have you searched for your problem: Yes
If so, what terms did you try: "You must include the text of your story either as an upload or as input into the textarea." then searched "curl" based on recommendations in the first threads I found.
State the nature of your problem: The site has been up since July 2013 without issue. Within the last 6 weeks or so, we have seen this error occur a few times when attempting to add a chapter of more than about 9800 words. If I click preview or add, the error message "You must include the text of your story either as an upload or as input into the textarea" appears, with all text removed from the story text box. Occasionally the word "curl" will be used in the chapter, but most often it is not. When I did find the word used, I tried removing it but got the same error. It's happened on my account and one other author I know of. It seems to occur inconsistently. For instance, the site would not allow me to add more than approx 9800 words, so I saved the chapter there, went back in later and tried adding the rest of the chapter, and it posted the entire chapter without problem (now 16,000 words). Sometimes that works and sometimes it doesn't. Sometimes I can post like 20k words in one go without issue. I've checked my forbidden words and text limits, and both are correct. It's driving me crazy now. 🙂 Any suggestions??
Do you have a test account for us? Yes
Account name: testuser
Password: 4LGR8TWmg8