I've also had that happen due to a post being moved.
Other times I've got that read-only message for legit messages that did not get moved. Go back to the post and reply again and the autosave still works. 
Chris
Please NO SD stretch-o-vision or 480 SD HD Channels
1-800-288-2020, After he gets acct info, press # a bunch of times, get a menu from Mr. Voice recognition
Your Results May Vary, In My Humble Opinion
I Call It Like I See It, Simply a U-verse user, nothing more
Award for Community Excellence (A.C.E.)
achiever for 2012*
*The views and opinions expressed on this forum are purely my own. Any product claim, statistic, quote, or other representation about a product or service should be verified with the manufacturer, provider, or party.