I also have had problems saving new messages, but only when I cut and paste from the screen above, usually when there is a link which is not translated. Nothing is saved. I didn't notice blanking of message text during saving either. I use Mozilla Firefox and the default skin.
Then it is probably gone now that I have disabled some UsabilityInitiative extensions. More details below. Raymond promised to look into it and report whatever he finds wrong. Confirmation appreciated.
# Usability Initiative extensions -- 2009-11-07 by Raymond #$wgUsabilityInitiativeModules = array( 'EditToolbar' ); #require_once("$IP/extensions/UsabilityInitiative/UsabilityInitiative.php"); #require_once("$IP/extensions/UsabilityInitiative/WikiEditor/WikiEditor.php"); #require_once("$IP/extensions/UsabilityInitiative/Vector/Vector.php");