If you enter a simple sentence or two in the editor it works fine. Try added several paragraphs (with or without code) and the error appears. 
that sounds to me like a probelm with the content column in the database, what is the data type for that column and the length set to?
Where it will take short data but not long, sounds like you may be using something like varchar (100) meaning it will accept up to 100 characters of variable character data.
you may want to change that column to varchar (500) or use the text data type.
for more on data types, see this page:
http://dev.mysql.com/doc/refman/5.6/en/storage-requirements.html
