Index: wp-content\themes\twentytwelve\style.css
===================================================================
--- wp-content\themes\twentytwelve\style.css	(revision 23244)
+++ wp-content\themes\twentytwelve\style.css	(working copy)
@@ -896,9 +896,14 @@
margin-top: 12px;
margin-top: 0.857142857rem;
margin-bottom: 12px;
margin-bottom: 0.857142857rem;
+ clear: both;
}
+img.alignnone {
+ clear: both;
+}
+
.entry-content embed,
.entry-content iframe,
.entry-content object,
.entry-content video {