Customers often cut-n-paste text or documentation into the Description or Notes fields. If the user then pastes the document into MS Word (or equivalent) the word or character count may show a much smaller number than 32768.
Note that Microsoft uses hidden characters which are proprietary to Microsoft that external applications have trouble interpreting. Agile Central does its' best to interpret these characters but often it is not 100% accurate. There can still be hidden or unrecognizable characters being entered into the field. These characters are still included in the description limit count. By pasting the description into a text editor (such as Notepad ++, Text Wrangler, Vim, Sunlime, etc. which are not word processing tools) searching for and removing all of the hidden characters and extra spaces you should have better luck saving it without any errors. Note that this includes formatting characters, bold, italics, tabs, etc.
These articles also have more information and ideas on how to troubleshoot this: