I have the following code at the top of my custom CSS. Obvious where it came from :) ...
Amazingly, having these comments causes about 100 lines of subsequent CSS to all be deleted?!!
This looks like a bug to me.
/*
THEME NAME: Sandbox
THEME URI: http://www.plaintxt.org/themes/sandbox/
DESCRIPTION: Rich with powerful and dynamic semantic class selectors, Sandbox is a canvas for CSS artists
VERSION: 1.6.1
AUTHOR: <a href="http://andy.wordpress.com/">Andy Skelton</a> & <a href="http://www.plaintxt.org/">Scott Allan Wallick</a>
AUTHOR URI:
TAGS: white, microformats, fixed-width, flexible-width, one-column, two-columns, three-columns, four-columns, left-sidebar, right-sidebar
*/
/* Customized by MrPete for my site */
/* Three column, sidebars on each side */
/* **********************************************
Font Size Settings
********************************************** */
/* There are several font size issues for variable size web display:
* IE's size cascade is broken in <=IE6
* Some versions of opera don't like 100%
* Some versions of Safari don't like 101%
*/
/* Fix IE, Opera, Safari bugs */
html,body {
font-size:100.01%;
}
(etc)