The discussions.apple.com text editor has a 5000 character maximum. If there are characters in your pasted text that the discussions text editor dislikes, it will throw that 5000 character max on you without you actually reaching the 5000 character limit. That is when you use the Additional Text tool on the editor's toolbar, or review your text content for certain characters (like phone numbers, for instance).
If you are posting text that is actually code, then use the </> code insertion tool on the discussions editor toolbar which usually masks illegal programming code symbols from the editor. Enter a final return, and click the </> again to turn it off.