I am also having this problem and cannot seem to get a solution.
The Text Changed Event is always fired on a postback whether the text was changed or not.
I trap the lengh of the text on page load and check it again when the user selects to exit the screen and even when nothing has changed the lengths are different.
I have even tried loading the FTB then getting its text length and again checking on exit they are still different?
Any insight to solve this would be greatly appriciated
Thanks
John