I never thought this will happen. I created a table by typing code into the WP post editor and clicked on visual to have a look, it was ok, when I clicked code tab again to continue with editing the table vanished, this happened for 5-6 times. 
WT#
Can’t create tables!!!
Posted by – December 12, 2008
Dude! I seriously don’t think it is that big a deal!
did you try by disabling visual editor?