( FIXED )
Users have reported that sometimes using the Spell Check is deleting the typed message.
We have been able to reproduce one scenario where this will occur, and it is a bug to be fixed. If you receive a plain text message, you click Reply (or Forward) and then you click "Color and Graphics" to change the message type, if you then use Spell Check the new text you entered will be deleted. In our testing if you simply reply and leave the message type as it was in the original (whether plain or html) then the problem doesn't occur.
If there are other scenarios where this problem occurs, please report them here.