[Plugin: NextGEN Gallery] NextGen gallery 1.9.6 lost its css styles

On a client’s web site, here, I had made some edits to nggallery.css to display her photos 3-up and to style the captions:

.ngg-gallery-thumbnail-box {
	float: left;
}
.ngg-gallery-thumbnail {
	float: left;
	margin-right: 10px;
	margin-bottom: 10px;
	text-align: center;
	width: 200px;
}
.ngg-gallery-thumbnail img {
	background-color:#FFFFFF;
	border:1px solid #A9A9A9;
	display:block;
	margin:4px 5px 4px 5px;
	padding:4px;
	position:relative;
}
.ngg-gallery-thumbnail span {
	/* Images description */
	font-size:90%;
	padding-left:5px;
	display:block;
	width: 200px;
	line-height: 125%;
	font-family: Arial, Helvetica, sans-serif;
	min-height: 60px;
}

It worked fine. Then the client updated the plugin to 1.9.6 on her own, and the css stopped working altogether; no floats, no styles at all. Inspecting the elements in Firebug showed no styles from nggallery.css at all.

I added the above styles to my site’s main css file, and it works again. But why did this happen, and is something broken in the install?

http://wordpress.org/extend/plugins/nextgen-gallery/